Add support for NSProgress #32

Make UZKArchive implement NSProgressReporting on OS X >= 10.11 and iOS >= 9.0, and support implicit progress reporting for earlier OSes.

https://developer.apple.com/videos/play/wwdc2015/232/

• Implement NSProgressReporting
• Add progress reporting to methods where it makes sense
• Update documentation for indicating progress reporting support
• Add progress reporting test cases
• Add overloads without progress block arguments and deprecate the old ones