refactoring test functions
parser comment
detect unused attrs in one more place, allow parsing to continue for all

changed a bunch of fatal()'s into err()'s, to allow parsing to proceed.
hygiene infrastructure.

- added a hash table to memoize rename and mark operations.
- added rename, mark, and resolve fold fns
getting rid of interner_key! macro
added and rewrote text for 'do' and 'for' loops
added new block expand fns
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