[groff] Double line table border for ASCII and UTF-8

[Pali Rohár]

Hi!

It looks like that both ASCII and UTF-8 output does not support double
line borders of table. Here is example:

$ cat test
.TS
box;
c.
Header
=
value1
_
value2
_
value3
.TE

$ man -Tutf8 ./test
┌───────┐
│Header │
├───────┤
│value1 │
├───────┤
│value2 │
├───────┤
│value3 │
└───────┘

$ man -Tascii ./test
+-------+
|Header |
+-------+
|value1 |
+-------+
|value2 |
+-------+
|value3 |
+-------+

But for DVI, PS and PDF output double line border between Header and
value1 is correctly rendered.

It is possible to support double line border also for ASCII and UTF-8
outputs? In ASCII I think that ======== can be used and for UTF-8 there
are Unicode glyphs box drawing glyphs also for double line.

-- 
Pali Rohár
address@hidden