Use v2.1.2 for dev
Dump debugger for byebug
Upgrade parslet to at least v1.6.1

It includes the optimization fixes so we don't need to monkey patch it
anymore

v1.6.1 and my optimization monkey patch do not play well with each
other, so lets use at least v1.6.1 and dump it
update changelog
Use correct terminology
Bump version for release
Test against 2.1.2
Stop testing against 1.9.3