added inputs for exercise 3

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

exercises/inputs/3_files_and_commands/A/letter.png

exercises/inputs/3_files_and_commands/A/piece-1.png

exercises/inputs/3_files_and_commands/A/piece-2.png

exercises/inputs/3_files_and_commands/A/tile-0.png

exercises/inputs/3_files_and_commands/A/tile-1.png

exercises/inputs/3_files_and_commands/A/tile-2.png

exercises/inputs/3_files_and_commands/A/tile-3.png

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

exercises/inputs/3_files_and_commands/C/letter.png

exercises/inputs/3_files_and_commands/C/piece-1.png

exercises/inputs/3_files_and_commands/C/piece-2.png

exercises/inputs/3_files_and_commands/C/tile-0.png

exercises/inputs/3_files_and_commands/C/tile-1.png

exercises/inputs/3_files_and_commands/C/tile-2.png

exercises/inputs/3_files_and_commands/C/tile-3.png

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

exercises/inputs/3_files_and_commands/D/letter.png

exercises/inputs/3_files_and_commands/D/piece-1.png

exercises/inputs/3_files_and_commands/D/piece-2.png