Integrate PSPDFKit

[brettcvz]

@steipete has generously offered to contribute a license of PSPDFKit, the best-of-all-possible PDF viewing/annotation frameworks. Integrating this should both dramatically improve the quality of the pdf experience and reduce the amount of code

[steipete]

Looking very much forward to have a port of ThatPDF with PSPDFKit to showcase both of our frameworks!
We're really close on releasing v3 with iOS7-support and lots of other improvements on annotations and PDF Forms, so this should be your starting point: http://customers.pspdfkit.com/demo

Let's discuss the rest via Email or Skype.