Previously, we had a custom method on the `TextMateBundle` class for
retrieving these variables from the bundle. Now we're using Atom's
`syntax.getProperty` mechanism. The idea is to map TextMate concepts
to their Atom equivalent, rather than building everything directly
around TextMate.
This makes the scoped property system mimic the behavior of CSS. When
there is a tie, the scoped properties loaded later in the cascade win.
I also optimize the scanning of all the properties, checking only those
sets of properties that have a value for the desired key path, to reduce
the need to match a ton of scope selectors.
We'll store all syntax-related global state in the `syntax` global. For
now, this means that all scoped properties will be stored here, as well
as all grammars.
