Consistent state of boolification---it builds!

Finished flock of theorems using new definition of wf_parser:
these live in DecodeScript.sml.

Big name change Boolify -> Encode.

Starting to encode variables.

Moved the code to automatically generate "boolify" functions for datatypes
from src/datatype/Datatype.sml to src/Boolify/src/Boolify.sml.

It uses the register_update_function hook to add the boolification
info (more on that later).

Also added a test suite for boolification.