Big fat update (read)

Two things you need to know about this:

1. This includes Chris' XCode updates and I've verified that after merging with my update, it does indeed compile and run on XCode6 Beta5. If you're hesitant or unable to switch compilers just yet, you can still pull this down and compile it on Beta4. It'll complain about a call to _bridgeToObjectiveC() -- just remove the leading underscore and it should compile.

2. This includes a switch to texture atlases and our new art pipeline. The commit comment explain what you need to know. Read them here:

https://github.com/jocelynlih/SwiftGameBook/commit/2cf29c69fbaae6a2f85a875c83ae824d511d6243