Added ast file

First part of it; trying to get type signatures figured out.
Program returns a list of all variables, including Players, and list of
Pieces.
Edited types in ast

Added game_t to be returned by program; Added coord_t; Added coordinate
to piece_t
Edited ast

Changed program type from string list * game_t list to a tuple of
strings list * game_t list
Edited parser

Finished setup, though it is likely unfinished

Questions about: using coord_t vs tuples, interleaving different types
of declarations; using actual integer values, like 0
Edited ast

Added rules_t
Edited Parser

Added rules section