Separating the library from the demo app

Hi,

I thought it would be more useful to have this project as an independent library, so I refactored the code so that you now have a PDF library along with demo app just depending and linking with it.

This will make it a lot easier to integrate in other projects, so that people can just use the library target as a dependency and keep up with new updates from the separate repository. I prefer this approach to just copying the files, personally, and it is probably cleaner.

Also centralized the resources in their own bundle (PDFReader.bundle) - may want to consider moving the strings files there too.