Regalloc fix: don't select a newly-freed register for a destruction-avoiding move
Move compiler/tokenize.mg -> compiler/liblex.mg
Update sprdpl and lexer API
Add str.count
Add filename/line-number tracking to lexer
Make truth semantics more Pythonic (objects without __len__ are True)
Add Function.__eq__
Add an error message for an unhandled __call__
Make sure dictionary items are iterated over in iterate_subtree
Allow __getitem__ to be overloaded
Update liblex API for token copying (still need special syntax...)
Add libparse.mg, basically a straight sprdpl clone
Update sprdpl