A major refactoring to the internals of how things work. I believe that
nothing is broken

The main refactoring here is removing the type field from the various
classes, but there are a few other smaller ones.

This also contains the grounds for a refactoring on variable use

Templates should now work, though there is no syntax to reference them
from rules yet

In addition, several internal things have been changed so as to improve
code quality

There is now syntax for rule references. Use @ instead of $, and use :=
to indicate you want exhaustion enabled

Use @ to refer to it

Case elements are now responsible for generating themselves.