added inputs for exercise 3

exercises/inputs/3_files_and_commands/A/image_tiling.json

+{
+  "name": "Image tiling",
+  "fws": [
+    {
+      "fw_id": 1,
+      "name": "Render an image from a character",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["character"],
+            "outputs": ["image"],
+            "command_spec": {
+                "command": [
+                    "convert", "-size", "800x800",
+                    "-background", "white",
+                    "-pointsize", "800",
+                    "-fill", "blue",
+                    "-gravity", "Center",
+                    "-trim"
+                ],
+                "character": {
+                    "binding": {
+                        "prefix": "caption",
+                        "separator": ":"
+                    },
+                    "source": {
+                        "type": "data",
+                        "value": "A"
+                    }
+                },
+                "image": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/letter.png"
+                    }
+                }
+            }
+          }
+        ]
+      }
+    },
+    {
+      "fw_id": 2,
+      "name": "Tile the image into four tiles",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["image", "tiled image"],
+            "command_spec": {
+                "command": [
+                    "convert",
+                    "-crop", "2x2@"
+                ],
+                "image": {
+                    "source": "image"
+                },
+                "tiled image": {
+                    "source": {
+                        "type": "data",
+                        "value": "/tmp/tile.png"
+                    }
+                }
+            }
+          }
+        ]
+      }
+    },
+    {
+      "fw_id": 3,
+      "name": "Rotate one tile 90 degrees clockwise",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["rotation angle", "piece 2"],
+            "outputs": ["top left"],
+            "command_spec": {
+                "command": ["convert", "-rotate"],
+                "rotation angle": {
+                    "source": {
+                        "type": "data",
+                        "value": 90
+                    }
+                },
+                "top left": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/piece-2.png"
+                    }
+                },
+                "piece 2": {
+                    "source": "piece 2"
+                }
+            }
+          }
+        ],
+        "piece 2": {
+            "type": "path",
+            "value": "/tmp/tile-0.png"
+        }
+      }
+    },
+    {
+      "fw_id": 4,
+      "name": "Flip another tile vertically",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["piece 1"],
+            "outputs": ["bottom right"],
+            "command_spec": {
+                "command": ["convert", "-flip"],
+                "bottom right": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/piece-1.png"
+                    }
+                },
+                "piece 1": {
+                    "source": "piece 1"
+                }
+            }
+          }
+        ],
+        "piece 1": {
+            "type": "path",
+            "value": "/tmp/tile-3.png"
+        }
+      }
+    }
+  ],
+  "links": {
+    "1": [2],
+    "2": [3, 4]
+  },
+  "metadata": {}
+}

exercises/inputs/3_files_and_commands/C/image_tiling.json

+{
+  "name": "Image tiling",
+  "fws": [
+    {
+      "fw_id": 1,
+      "name": "Render an image from a character",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["character"],
+            "outputs": ["image"],
+            "command_spec": {
+                "command": [
+                    "convert", "-size", "800x800",
+                    "-background", "white",
+                    "-pointsize", "800",
+                    "-fill", "blue",
+                    "-gravity", "Center",
+                    "-trim"
+                ],
+                "character": {
+                    "binding": {
+                        "prefix": "caption",
+                        "separator": ":"
+                    },
+                    "source": {
+                        "type": "data",
+                        "value": "C"
+                    }
+                },
+                "image": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/letter.png"
+                    }
+                }
+            }
+          }
+        ]
+      }
+    },
+    {
+      "fw_id": 2,
+      "name": "Tile the image into four tiles",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["image", "tiled image"],
+            "command_spec": {
+                "command": [
+                    "convert",
+                    "-crop", "2x2@"
+                ],
+                "image": {
+                    "source": "image"
+                },
+                "tiled image": {
+                    "source": {
+                        "type": "data",
+                        "value": "/tmp/tile.png"
+                    }
+                }
+            }
+          }
+        ]
+      }
+    },
+    {
+      "fw_id": 3,
+      "name": "Rotate one tile 90 degrees clockwise",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["rotation angle", "piece 2"],
+            "outputs": ["top left"],
+            "command_spec": {
+                "command": ["convert", "-rotate"],
+                "rotation angle": {
+                    "source": {
+                        "type": "data",
+                        "value": 90
+                    }
+                },
+                "top left": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/piece-2.png"
+                    }
+                },
+                "piece 2": {
+                    "source": "piece 2"
+                }
+            }
+          }
+        ],
+        "piece 2": {
+            "type": "path",
+            "value": "/tmp/tile-0.png"
+        }
+      }
+    },
+    {
+      "fw_id": 4,
+      "name": "Flip another tile vertically",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["piece 1"],
+            "outputs": ["bottom right"],
+            "command_spec": {
+                "command": ["convert", "-flip"],
+                "bottom right": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/piece-1.png"
+                    }
+                },
+                "piece 1": {
+                    "source": "piece 1"
+                }
+            }
+          }
+        ],
+        "piece 1": {
+            "type": "path",
+            "value": "/tmp/tile-3.png"
+        }
+      }
+    }
+  ],
+  "links": {
+    "1": [2],
+    "2": [3, 4]
+  },
+  "metadata": {}
+}

exercises/inputs/3_files_and_commands/D/image_tiling.json

+{
+  "name": "Image tiling",
+  "fws": [
+    {
+      "fw_id": 1,
+      "name": "Render an image from a character",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["character"],
+            "outputs": ["image"],
+            "command_spec": {
+                "command": [
+                    "convert", "-size", "800x800",
+                    "-background", "white",
+                    "-pointsize", "800",
+                    "-fill", "blue",
+                    "-gravity", "Center",
+                    "-trim"
+                ],
+                "character": {
+                    "binding": {
+                        "prefix": "caption",
+                        "separator": ":"
+                    },
+                    "source": {
+                        "type": "data",
+                        "value": "D"
+                    }
+                },
+                "image": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/letter.png"
+                    }
+                }
+            }
+          }
+        ]
+      }
+    },
+    {
+      "fw_id": 2,
+      "name": "Tile the image into four tiles",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["image", "tiled image"],
+            "command_spec": {
+                "command": [
+                    "convert",
+                    "-crop", "2x2@"
+                ],
+                "image": {
+                    "source": "image"
+                },
+                "tiled image": {
+                    "source": {
+                        "type": "data",
+                        "value": "/tmp/tile.png"
+                    }
+                }
+            }
+          }
+        ]
+      }
+    },
+    {
+      "fw_id": 3,
+      "name": "Rotate one tile 90 degrees clockwise",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["rotation angle", "piece 2"],
+            "outputs": ["top left"],
+            "command_spec": {
+                "command": ["convert", "-rotate"],
+                "rotation angle": {
+                    "source": {
+                        "type": "data",
+                        "value": 90
+                    }
+                },
+                "top left": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/piece-2.png"
+                    }
+                },
+                "piece 2": {
+                    "source": "piece 2"
+                }
+            }
+          }
+        ],
+        "piece 2": {
+            "type": "path",
+            "value": "/tmp/tile-0.png"
+        }
+      }
+    },
+    {
+      "fw_id": 4,
+      "name": "Flip another tile vertically",
+      "spec": {
+        "_tasks": [
+          {
+            "_fw_name": "CommandLineTask",
+            "inputs": ["piece 1"],
+            "outputs": ["bottom right"],
+            "command_spec": {
+                "command": ["convert", "-flip"],
+                "bottom right": {
+                    "target": {
+                        "type": "path",
+                        "value": "/tmp/piece-1.png"
+                    }
+                },
+                "piece 1": {
+                    "source": "piece 1"
+                }
+            }
+          }
+        ],
+        "piece 1": {
+            "type": "path",
+            "value": "/tmp/tile-3.png"
+        }
+      }
+    }
+  ],
+  "links": {
+    "1": [2],
+    "2": [3, 4]
+  },
+  "metadata": {}
+}