Swift

Here's a complete guide on the basics of Swift. I know @golergka already has a [PR](https://github.com/adambard/learnxinyminutes-docs/pull/634) on the way but I think this guide has a more complete version of Swift. Some of our examples are the same, but I've condensed the examples so that only brand new information is shown in each code snippet.

Aside: @gizmo385 referred me here after seeing my [swift cheat sheet](https://github.com/grant/swift-cheat-sheet)