Add MuPDF support to cups-filters for a lightweight mobile printing stack

The current PDF renderer in cups-filters, namely Ghostsscript and Poppler, are much heavy weight to mobile devices as compared to MuPDF which is significantly lightweight. Implementation of MuPDF is required in the cups-filters as it will save lots of memory, storage and CPU resources in mobile devices for printing job. Filters like pdftops, pdftoopvp, pdftoraster, pdftoijs and pdftopdf have to be modified in order to add support for MuPDF without dropping existing support for Ghostscript and Poppler.