Note that all `charXXX' entity names have been removed from the font files.
They don't make sense for Unicode.

The following from the original troff manual (by Ossanna and Kernighan) is
unmapped:

  \(bs    shaded solid ball (Bell System logo, AT&T logo)

Character 0x002D has not been given a name because its Unicode name
"HYPHEN-MINUS" is so ambiguous that it's unusable for serious typographic use.

The following, mentioned in the original troff manual, are only approximate:

  \(lk    middle part of big left curly brace
  \(rk    middle part of big right curly brace

\(wp has been mapped to 0x2118, because according to unicode.org's
NamesList-3.0.0.txt, U+2118 "SCRIPT CAPITAL P" is really a Weierstrass p,
neither SCRIPT not CAPITAL.

The following line could be added; "space" is known to "devps" but are not
documented and not known to "devdvi" (actually, there is no space glyph
within the TeX system).

space	24	0	0x0020

The following lines could be added, to define names which are known to e.g.
"devdvi" but are not known to "devps".

<<	24	0	0x226A
>>	24	0	0x226B

"devps" maps \(a~ and ~ to asciitilde, which is equivalent to 0x02DC, but
this glyph is just too small.  We map them to 0x007E instead.

"devps" maps \(a^ and ^ to circumflex, which is equivalent to 0x02C6, but
this glyph is just too small.  We map them to 0x005E instead.

"devps" maps *U to Upsilon1, which is equivalent to 0x03D2.  We map it to
0x03A5 instead.

"devps" maps *W to Omega, which is equivalent to either 0x2126 or 0x03A9.
We map it to 0x03A9.

"devps" maps *D to Delta, which is equivalent to either 0x2206 or 0x0394.
We map it to 0x0394.

"devps" maps CR to carriagereturn, which is equivalent to 0x21B5.  We map
it to 0x240D instead.


Using unnamed characters
------------------------

Assume you want to use a Unicode character not provided in the list, say
U+20AC. You need to do two things:

- Add a line

    ---	24	0	0x20AC

  (the second column is computed as 24 * wcwidth(0x20AC)) to the file
  R.proto, or, when groff is already installed, to the four fonts files in
  $(prefix)/share/groff/<version>/font/devutf8/.

- In your source file, use the notation \N'8364' where 8364 is the decimal
  representation of 0x20AC.
