Add detection for the XC programming language.
Add .pyt as an extension for Python
Languages.yml entries must be in alphabetical order
Added .tmTheme as XML extension

Files with the `.tmTheme` extension similar to `.tmCommand`, `.tmLanguage`, `.tmPreferences` and `.tmSnippet` are configuration XML files for TextMate or SublimeText.

The `.tmTheme` extension was missing from this list.
Merge pull request #377 from rlsosborne/detect-xc-language

Add detection for the XC programming language.
Merge pull request #543 from jasonbot/master

Treat `.pyt` files as Python source
Merge pull request #541 from hkdobrev/patch-1

Added .tmTheme as XML extension