Replace the empirical GhostScript-derived font metrics with ones derived

Replace the empirical GhostScript-derived font metrics with ones derived
from Adobe's official AFM files.  These are expressed in integer multiples
of 1/1000 pt (well, 1/1000 of the design size of the font, actually, but that's
always a whole number of points), so use that as our internal unit rather
than 1/4096 pt.  This doesn't seem to make a significant difference to
Halibut's output.

git-svn-id: svn://svn.tartarus.org/sgt/halibut@4576 cda61777-01e9-0310-a592-d414129be87e