[Redesign] Added the concept of "Code Generator"

Notes:
      - Needs tests, Pradyun is on it!
      - Needs to be implemented

Translators shall now only exist for languages we intend to convert to
the AST, i.e. only Python (currently).
A Code Generator
   - converts the AST into source code.
   - lives as a module or package within "py2c.code_generators"
   - Inherits from "py2c.base_codegenerator.AbstractCodeGenerator"
   - More details to be discussed and decided.