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)
added and rewrote text for 'do' and 'for' loops
added new block expand fns
tmp
changing to newer macro escape mechanism, using uints in more places
comments & whitespace