Remove unused constant
Let the user know which files are added to MSpec (grossly)
Extract ParserHelper to spec/support
Add an mspec_rspec_adapter tu run parser specs in mspec
Fix StringScanner#[] to return nil for missing match.

This was causing a bug running our stringscanner implmentation in
javascript as `undefined` was slipping into the lexer/parser from this
method.
Ensure specs are ran in an UTF-8 encoded page
Numeric#chr takes an encoding argument

Currently it will be ignored.
Add StringScanner failing specs to bugs

Emerged after fixing the encoding of the phantomjs runner page.
Add StringScanner#string