change to newer macro escape mechanism, using uints in more places
comments & whitespace
starting to add sexp encoder
part of macro scoping redesign
move stmt expansion code
bugfixes, add get-names-from-pattern fn (and test case)
working on adding let-renaming
parser comments
adding fresh_name_fn
bugfixing
removed obsolete reference to purity
rename repr to name
removed some interner fields
changed representation of some tokens to be just interned strings rather than idents

also, clean up unused pass-around-interners
@ -> & on strings
uint/name type error fixes