Break Infinite Loop, Smoke Test.

- Stop the Lexer from wreaking havoc.
- Stop the Parser from infinite loops and falling
  back to parsePara.
- Corrected logic of `ParserBase.prototype.shiftUntil()`.
- Renamed `ParserBase.nestlvl` -> `ParserBase.currlvl`
- Added some guards in case `ParserBase.options` is just
  a plain object. Also modified the module to pass the
  options into the parser.