TODO

Clean up metacompiler.

Some mechanism for hooking in compilation wordlists.  Also for
metacompilation.

Make backtrace more useful by searching all vocabularies.

Separate XT from NT.  Make XT point directly at code field.

Rearrange header.

Add UM/MOD and friends.

Pass Hayes' CORE tests.  Then COREEXT, TOOLS, STRING, EXCEPTION,
SEARCHORDER, DOUBLE, etc.

Finish PDP-1 target.

Finish shell script and batch file targets; use them for bootstrapping.

Retire Lisp metacompiler.

More Forth2012 words.

Clean up quotations and move to libraries.

Clean up LATER> and move to libraries.

Create STC x86 target?  With inlining?

Metacompile FIG-Forth model (create 6502 simulator, etc).