Periodic cleanup and refactor

It's been a while since the codebase has been reviewed in depth. I'll be going through the RangeCollection class to remove unused/deprecated features, add documentation where needed, and do some general cleanup.

There are likely many low-level methods that may be removed; I'll identify all features used directly in the linref package to determine what can be removed/modified without impact and what may need an associated version requirement on the next rangel and linref releases.