Update Packages and add support for clear_scopes

[trishume]

• Update the Sublime Packages submodule to the latest version
• Add clear_scopes to the SyntaxDefinition type
• Fix test failures due to updated syntaxes
• Implement the new clear_scopes setting in the parser
• Benchmark and ensure that performance hasn't regressed.

I'm currently waiting on a reply to my comment on sublimehq/Packages#466 to see if I understand clear_scopes before implementing it. I'm planning on storing a Vec<Scope> in StateLevel of scopes to push back on to the stack when that level is popped.

fixes #26

cc @robinst

[trishume]

So I ran some benchmarks and it seems that these changes come with a 4% performance regression with the same version of the JS sublime-syntax, and an 8% regression comparing this branch to master including the newer JS sublime-syntax. The new syntax has more features and gives better results so I think the 4% is a better number, and I think that's acceptable. I'll also try running the other benchmarks.

[robinst]

Would you mind cutting a release with these changes included (probably 1.1.0)? Switching over the regex engine might take a while :).

[trishume]

@robinst done.

[robinst]

Thanks, works nicely!