Store types in intermediate representation

[Liudmila Kornilova]

typeUsesOtherType function checks if type is used in other type by simply comparing strings.
This approach will fail on more complex types.

It would be better not to convert a type directly to string but to store it in intermediate representations.
There will be a class Type that stores either string (for example native.CInt) or a pointer to other IR instance: Struct, Union or Enum.

Also there will be following subclasses of Type:

• PointerType
• ArrayType
• FunctionPointerType

All above classes will store pointer(s) to other types