Don't try to register the two fonts Dingbats.cff and StandardSymL.cff
with crengine because it will reject them anyway. But we cannot simply
remove these two fonts because they are used internally by mupdf to
emulate "builtin" fonts which are mandated by Adobe PDF specification to
be present in every valid implementation.
a bit of cleanup, switched width/height combo over to use
Geom() objects, moved framebuffer handling to Screen object,
callback syntax sanitizing, lots of small changes
