r?
Apply deriving_eq to the data structures in ast.rs, and get rid of the custom definitions of eq that were everywhere. resulting ast.rs is about 400 lines shorter.
Also: add a few test cases and a bunch of comments.
Also: change ast_ty_to_ty_cache to use node ids rather than ast::ty's. I believe this was a suggestion related to my changes, and it appears to pass all tests.
Also: tiny doc fix, remove references to crate keywords.
6efa3543a8