Adjusted parameters for all Environment functions

Makes more sense to have the environment object passed as the first
parameter for all the functions. At the very least, it's nice for a
bunch of functions that all take that value to take it in the same-ish
position.
Added Evaluation module

Just has a few things in it for now so we can test declaring, setting,
and retrieving values.
Rebuilt interactive, added parsing var expressions

Includes the same as the Evaluation module: declaration, assignment,
and retrieval.