Better scopes for "async def"; Add all built-in exceptions and warnings.

[1st1]

This PR changes the implementation of async/await support.

Instead of classifying 'async' as a 'storage modifier' keyword, it is now correctly classified as a 'control flow' one.

'async def' must be parsed as part of "function.python" scopes, in order for ⌘R to work correctly.

Please see the attached screenshots of how the changes look on real code.

One more detail: the PR updates the list of built-in exceptions & warning classes. It also stops highlighting /(\w+)Error/ kind of exceptions as built-ins.

P.S. This is a second PR -- the first one was against the master branch by accident.

[MattDMo]

Looks good. Why did you remove async from invalid.illegal.name.python?

[1st1]

Looks good. Why did you remove async from invalid.illegal.name.python?

Because when you start typing 'async' it flashes it as invalid, and then it only becomes properly highlighted once you finish typing def, with or for. In some colour schemes, invalid scope is super prominent (in mine it's red background and white foreground), so it's very annoying.

BTW, I'm currently using the unicode branch with this commit on top, and it highlights all my source code just fine. I think it's ready for merging into master.