todo

早期freebsd实现

Read PFB files directly.

Generate %%DocumentMedia comment.

For efficiency it might be better to have the printer interface have
support for the t and u commands.

Angles in arc command: don't generate more digits after the decimal
point than are necessary.

Possibly generate BoundingBox comment.

Per font composite character mechanism (sufficient for fractions).

Consider whether we ought to do rounding of graphical objects other
than lines. What's the point?

Error messages should refer to output page number.

Search for downloadable fonts using their PostScript names if not
found in download file.

Separate path for searching for downloadable font files.

Clip to the BoundingBox when importing documents.