Enumerations

[panagosg7]

Addessing #55

For an enumeration

enum E { ADD, SUB, MUL, DIV } 

E has type enum E, E.ADD has type { number | v = 0} etc.

Also, E[0] resolves to a string type: { string | v = "ADD"}

Added some fixes in unification / subtyping:

• module m, class c and enum e are all types that get flattened to an object literal type if needed. This follows TS behavior.

[ranjitjhala]

Awesome, thanks!