Array data structure

It is already used as output from Table and Series with the array property. What is missing is

1. Grammar rule for array literals
2. Type and typecheck
3. Value and value (runtime) type check
4. Formatter

In addition, there should be BoolArray, StrArray, IntArray and FloatArray (later on ComplexArray). Currently only Array and FloatArray are in types.py and in serializable.py.