Sync Xcode snippets

[ryanmasondavies]

I'd love to be able to sync my Xcode snippets using git. I don't really use my snippets as it stands because they're not available on all of my computers.

Some notes on this:

• There's a command line interface for installing Xcode snippets here. The files are stored as *.m / *.swift files with YAML front matter for meta info. I've experimented with Xcode's snippets folder - each snippet is given a unique identifier. As such this task wouldn't be as simple as putting the Xcode CodeSnippets under git.
• Xcode snippets should be stored in a separate repository and pulled into this one as a submodule.
• xcode/install.sh should include a script to run through all code snippets and install them automatically. (Delete old ones as necessary.)