Better CFG Syntax

[LeoWoerteler]

The syntax for specifying the context-free grammar isn't very expressive, some enhancements would be:

• allow grouping, optional parts (?) repetition (* and +) in right-hand sides (RHS) of rules:

  A -> (B C?)+ D*

• more than one RHS, separated by e.g. |:

  Lit -> NumLit
       | StrLit