Reimplement lookups, getters, setters, encoders

While working on adding batch operations (RedisObjectStream), I realized
that I should have structured the classes all differently. Having both
lookups and Redis types implemented as their own classes would let me
encapsulate all the needed information on each class.

This (mostly) completes the reimplementation. I *think* this is an
improvement? It's easier to reason about, but I don't think the
_RedisType class and subclasses always follow the LSP. Specifically,
different subclasses expect different data types when using 'set'. It
works, so I'm calling it done. If we ever go back and implement type
hints and such, then we may need to rethink some things.

Author: jthomale