todo

早期freebsd实现

Dotted and dashed ellipses.

In troff mode, dotted and dashed splines.

Make DELIMITED have type lstr; this would allow us to give better
error messages for problems within the body of for and if constructs.

In troff mode without -x, fake \D't' with .ps commands.

Perhaps an option to set command char.

Add an output class for dumb line printers. It wouldn't be pretty but
it would be better than nothing. Integrate it with texinfo.  Useful
for groff -Tascii as well.

Option to allow better positioning of arrowheads on arcs.

Perhaps add PostScript output mode.

Change the interface to the output class so that output devices have
the opportunity to handle arrowheads themselves.

Consider whether the line thickness should scale.

Consider whether the test in a for loop should be fuzzy (as it
apparently is in grap).

Possibly change fillval so that zero is black.

Provide a way of getting text blocks (positioned with `.in' rather
than \h), into pic.  Should be possible to use block of diverted text
in pic.  Possibly something similar to T{ and T} in tbl.

Option to provide macro backtraces.

Have a path that is searched by `copy' statement.  Set by environment
variable or command line option.