803b37597e
Document `InferTy` & co. I finally figured out what `TyVid` means! The name is quite opaque, so I decided to document it and related types. I don't know that much about `InferTy` & co., but I was able to *infer* ( :) ) from the names and what I know generally about type inference to add some basic documentation.
For more information about how rustc works, see the rustc dev guide.