hygiene
probably better behavior when encountering a wholly unexpected token
plausible tokens for a given state
fixing a JS crash with a nullable production rule
adding support for error-priorities in syntax of BNF.  it's not quite
working yet, but it parses
getting error parsing to work.  still not using the priorities yet,
but at least not crashing on right-nullable entries
Merge branch 'new-world' into ungrammar2
Merge branch 'new-world' of github.com:brownplt/pyret-lang into ungrammar2
unnecessary file
minor edits around setting up ungrammar
just mucking around for now; this is somewhat broken (hence branch)