Page Numbering and fixes

The CombinePDF library is becoming more and more a: PDFTookit library...

for example: ...now, we can number pages, add opaque/transparent text-boxes (with nice borders and backgrounds)...

There is even a nice Font library object (now containing only the 14 standard fonts) which could help with multilingual page numbering formats (such as non-latin page numbers. I hope one day we format page numbering as "page number: %d of 1032" in Russian).

There is still an issue with "stamping" some PDF pages (overlaying one PDF page over another), but the library is progressing nicely.

Filter support is still very basic, but it seems that all the PDF files I have tested with are within the spectrum of this limited filter support.

This versions seem ready for combining PDF files (one after the other) and adding page numbers... Please test before using and let me know if you find any issues.