Feature: XML Theme and Grammar support

[glennsl]

Brings in the changes onivim/reason-textmate#54 and onivim/reason-textmate#55 which added parsing of XML grammars and themes, respectively, to reason-textmate.

Has so far been tested to work with:

• https://github.com/chiragpat/tomorrow-and-tomorrow-night-operator-mono-theme
• https://github.com/glennsl/vscode-duotone-dark-faithful
• https://github.com/JustusAdam/language-haskell

Let me know if there's anything else we should test.

Fixes #912
Probably fixes #1486
Addresses #1471, but does not completely fix it. See comment below

[glennsl]

https://github.com/vscode-restructuredtext/vscode-restructuredtext fails with "invalid backref number/name". Seems like a regex issue.

[bryphe]

https://github.com/vscode-restructuredtext/vscode-restructuredtext fails with "invalid backref number/name". Seems like a regex issue.

Interesting... yes, seems unrelated to the new parsing logic (unless there's some sort of weird string escaping happening). But this seems unlikely since there are tests that would cover this. Must be exposing a pre-existing bug in our regex handling.

[bryphe]

I get to test out the Duotone themes now! 🎉

[glennsl]

https://github.com/SuperiorServers/vscode-glua fails because it doesn't have a repository

[glennsl]

After making repository optional, that one fails with "invalid backref" too.

[glennsl]

I created a PR for the invalid backref problem at onivim/reason-textmate#57. I see no reason it should block this though.

[bryphe]

I created a PR for the invalid backref problem at onivim/reason-textmate#57. I see no reason it should block this though.

Thanks for looking at this! Agreed, not blocking 👍