Tracking issue for macro compiler

[sdleffler]

This is a tracking issue for the macro-compiler-dev branch (PR #36).

• Allow the user to omit commas for some statements of split/choose/offer constructs (Optional comma omission in Session! macro's choose/offer/split statements #45)
• Enumerative testing of the full macro compiler (nice to have but not necessary) (Enumerative and random testing for macro compiler #40)
• Random testing of the parser (Enumerative and random testing for macro compiler #40)
• Analyze control flow to report unreachable code and unproductive loops which would produce odd type errors (Control flow analysis pass for macro compiler #41)
• Write missing internal documentation for large and complex functions, especially transformations of the CFG
• Write README documenting the whole compiler, including CFG passes and what they do/how they work and what invariants are upheld