Define entrypoint to change grammars to be tight/loose equality

Existing entrypoints change the global grammar; new functions make it
easy to adjust arbitrary grammar values.

Make ParseExtras.condprinter visible in signature.

This helps when working around gihub issue #367.

Provide more options for futzing with ='s precedence

Now there are four functions:

{temp,}_{tight,loose}_equality

The temp versions create an effect that is not exported in the theory
file, and can be called before new_theory without causing annoying
error messages about changes being discarded.

The tight precedence is 450, which is the same level as the other
standard relational operators (e.g., <). The loose precedence is 100,
which is historical, and clearly appropriate for = construed as iff.

Change src/bool to src/1 as a prelude to experimentation!