Optimise grammar and correct property scopes

[Alhadis]

To make the maintainer's life easier, I...

• [x] created at least 1 spec to cover my changes, Well, there were no specs for the grammar to begin with, so I'm naïvely assuming it won't be necessary. =)
• [x] npm tested my code and it's green like an :green_apple:, Greener than any emoji.
• [X] adjusted the readme.md, if it was necessary and Nope, not needed
• [ ] would like to receive get a :beer: or :coffee: after that hard work! I don't drink alcohol, and I'm adequately caffeinated.

Resolves #115.

This could actually be optimised even further in size, but I'm assuming the pattern placement is deliberate (e.g., highlighting keywords only in the context of their relevant properties). I've therefore left it as-is.

[florianb]

@Alhadis thank you very much! I didn't know the mode-modifiers do work for js-regex (and or naively assumed Atom relies on the js-engine). I test and approve it as soon as possible! 👍

[Alhadis]

Atom doesn't use JavaScript's crappy regex for syntax highlighting, heh. It uses the Oniguruma engine, which is also used by Ruby and TextMate. =)

And no problem, my pleasure. 👍

[florianb]

Hah! These are great news! 👏