Completely revised support for conversion of TTFs to T42 fonts.

Completely revised support for conversion of TTFs to T42 fonts.

. In print_header(), the various dictionary values are now correct;
they have been incorrectly scaled.  The font revision value is now
handled as a 16.16 fixed-scale value.

. t42_write_table() (which was only present in Han-Wen's git branch)
has been completely rewritten; as can be seen, much more has to be
done than previously expected...  I've changed the layout of the
/sfnts array to use the same format as FontForge; this has helped
a lot during debugging.

. It was necessary to extend print_body() a lot; we have to
construct our own TTF header.  It is perhaps overkill to compute
the correct checksums, but...

. Glyph index 0 is now always called `.notdef'.