This makes the two maps in GenerationState private. Use the
defineVar/findVar or defineRuleVar/findRuleVar instead.

This is another change on the way to doing autovivify

Logging now uses the RGrammarLogging system so as to allow for better
customizability of how the logging works

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

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

More work that leads towards getting templates working

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

Use @ to refer to it