Implement Copland Abstract Syntax Coq library/module

[ampetz]

Refactor the copland-avm Coq specification to pull out the Copland Abstract Syntax into its own library (module?) and allow it to be imported to separate projects via something like Opam.

Users should be able to import specific versions easily via this mechanism. (i.e. import Copland_AST_V1, V2, ...)