Port wkpdf to Swift or Objective-C

[plessl]

wkpdf builds on RubyCocoa, which has been abandoned by Apple in OS X 10.9. Hence, I will stop the support and development of the RubyCocoa version of wkpdf.

There has been a predecessor version to wkpdf, which was implemented in Objective-C. I'm considering porting wkpdf either back to Objective-C or to Apple's new programming language Swift.

If anybody is interested in contributing to this effort, please let me know.