Swift 3 Support

[cemolcay]

Hi, are you considering adding the swift 3 support soon?
If not, I can push you a pull request if you open a swift3 branch.

[joshgare]

I second this, with the release on Xcode 8.3 this library will no longer compile. Although for those looking for a quick fix, you can just convert the HorizontalFloatingHeaderLayout target by going to Edit > Convert > To Current Swift Syntax. After this process has completed just apply all the fixes suggested by the Issue navigator and everything will work from this point onwards.