[Groff] \~ in \X for grohtml

[Werner LEMBERG]

Gaius,


right now I've changed the \X command to ignore `\&', `\%', `\)', and
`\:' (for all devices).  While doing this I've found a small omission:
`\~' and `\ ' aren't handled properly.  IMHO both tokens should be
converted to ` ' if processed with -Thtml.

Similarly, \e, \E, \C, and \N should be supported for -Thtml since all
those escapes produce glyphs.  What do you think?  BTW, the following

  .URL www.xxx.org "This\C'hy'is a test"

causes a fatal bug with -Thtml:

  post-grohtml: Failed assertion at line 106, file
                `src/libs/libgroff/nametoindex.cc'.


    Werner