checkpoint, add open types to grammar
fix MethodsFinder
fix grammar, add test
checkpoint for open types

Mostly working, though I need to get Tokens all the way through for
error messages.
get token info to where it's needed for errors
fix test
test method invocation on open type

As expected, this "just works" because of how open types are expanded
and treated like normal alias types after their invariants are checked.
Merge branch 'open-types-2'