Apple's Swift plugin for Vim

This is a copy of Apple's Swift tools for Vim from their Swift repo. I've put it in a separate repo so that you can easily install it with your prefered plugin installer. (I use Vundle, so I just add Plugin 'jph00/swift-apple' to my .vimrc and run :PluginInstall.)

It provides syntax highlighting for gyb, SIL, and Swift files, and sets defaults for tab stops etc.

I've also added syntax highlighting for gyb templates for C and header files.