* Cleaned up tokenizer to make subsyntax operations more clear.
* Explanatory comments.
* Made it so push_subsyntax could be safely called elsewhere.
* Unified terminology.
* Minor bug fix.
* State is an incredibly vaguely named variable. Changed convention to represent what it actually is.
* Also changed function name.
* Fixed bug.
* Only one highlighter state is kept per-document as opposed
to one per-docview
* Fixes a bug with retaining older highlighter state as a
DocView wasn't able to detect lines changing above it's viewport
* Renames `highlighter` module to more descriptive `tokenizer`