Pascaligo improvements

[RunDevelopment]

Hello @DefinitelyNotAGoat!
While reviewing your branch I also implemented a few improvements while I was at it. This should also address all of my comments here.

There is one major change which is that I removed the variable token. I did this for 2 reasons:

1. Prism's highlighting should be consistent. Variables were only highlighted at definition but not usage.
2. It doesn't improve readability because everything which is neither comment nor string nor keyword nor literal nor punctuation/operator is a keyword. Basically, everything which was and was not highlighted as variable is a variable.

I hope that that's ok with you.

Btw. The examples in the LIGO repo are quite useful for testing.

[DefinitelyNotAGoat]

Thanks @RunDevelopment! Admittedly, regular expressions are not my strong suit, so I really appreciate this.