* Fix ast.GroupDefinition.glyphSet() by using ast.GlyphName,
ast.GroupName and ast.Range in Parser.parse_coverage_(), and making it return
ast.Enum.
* Add ast.Enum.__len_() to fix the calculation of max_src and max_dest
in Parser.parse_substitution_(). I’m not sure I understand the logic
of this many to many check, will double check later.
* Update the test suite to reflect this. Had to add ast.Enum.__eq__() to
make it less painful, and __hash__() as otherwise ast.Enum wouldn’t be
used as a key in dicts (not sure this is a goo idea either, will
double check later).