Use DOMPDF_FONT_CACHE for new/remote fonts

So DOMPDF_FONT_DIR only contains the provided fonts and does not have to be writeable
Merge remote-tracking branch 'upstream/master'
Merge branch 'master' of https://github.com/VIISON/dompdf into VIISON-master
Improve font management

DOMPDF_FONT_DIR can now be customized so that fonts can be stored
outside the dompdf installation directory. The fonts included
with dompdf are now hard-coded so that they are always available.
Updating distributed font family cache after font management update
Merge branch 'font-management-tweak'