Clean up grammar source

[Alhadis]

Trivial changes to code formatting that were prompted by feedback to an earlier PR.

Summary:

• Simplified character classes for matching variable names:

  [a-zA-Z_$][a-zA-Z_$0-9]*
  [a-zA-Z_$][\\w$]*
  

• Extended patterns now use triple-quoted blocks consistently

• Lengthy patterns converted into extended patterns to clarify

[winstliu]

I don't think these spaces are needed, right?

[Alhadis]

Nope. The space only serves to distinguish one column from another:

Of course, I can always remove it if you prefer. I just found it pronounced the pertinent parts better for new readers.

[Alhadis]

@50Wliu I've shot the spaces into orbit, disregard my earlier comment. =)

[Alhadis]

@MaximSokolov Can you check if there're any conflicts between this PR and #408?

[Alhadis]

... okay, I literally asked that the same time you submitted your PR to my branch. Flawless timing.

@50Wliu There're keywords missing from the support-constant groups, which I'm planning on submitting in a follow-up PR (which fixes a few other bugs as well). I've isolated all cosmetic changes to this branch in an effort to keep a cleaner revision history.

I also fixed a few typos in the matching groups and eliminated the nested subpatterns. Oniguruma processes fixed-length lists faster than nested ones, so stuff like borderWidth|borderHeight|borderColour will match faster than border(?:Width|Height|Colour) or what-have-you. I benchtested this myself, although I've forgotten what grammar/repo I did it in...

[MaximSokolov]

There is no conflict

[Alhadis]

Stellar. Спасибо!