Update token capitalization & usage

# Overview
Upstream changes to naming / tokenizing made things easier, but
necessitated changing the token analysis code. Some legacy manual
span analysis code may still exist.

# Notable changes
Most things are just renames - pretty straight-forward.

Only thing that really changed was one logic check to check for `[]` delimiters in the generator macro. I had to change the checking to an if statement, to avoid copying referenced fields out of the `Delimiter` parameters.

# Caveats
Since the upstream changes are post-0.12, you'd have to have a recent version of rust for this to work. We could try to support older versions, but hey, this is rust, where we throw away all legacy support at the moment.
This can be removed in favor of using the `TokenTree::get_span` method.