Illegal Syntax exceptions

If you try to use "illegal" syntax, like /(?=lookahead)/.examples, the gem will now raise an exception.
This is not yet implemented for unsupported syntax like /\p{Arabic}/.examples; this will be added in the next release.

There is also a MAJOR re-write of how capture groups and backreferences are managed in the backend. This was mainly just a code clean-up, although it does provide some user benefits which I have yet to document.