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.
added rename, mark, and resolve fold fns
getting rid of interner_key! macro
starting to add sexp (now rotted, sigh)
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added and rewrote text for 'do' and 'for' loops
working on expand
comments & whitespace
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