[Groff] New escape sequence `\$^'

[Werner LEMBERG]

To make trace.tmac handle .nr, .ds, .as, and friends, I've added a new
escape sequence.  From groff.texinfo:

  -- Escape: \$^
     Handle the parameters of a macro as if they were an argument to the
     `ds' or similar requests.


          .de foo
          .  tm $1=`\\$1'
          .  tm $2=`\\$2'
          .  tm $*=`\\$*'
          .  tm address@hidden@'
          .  tm $^=`\\$^'
          ..
          .foo " This is a "test"
              => $1=` This is a '
              => $2=`test"'
              => $*=` This is a  test"'
              => address@hidden" This is a " "test""'
              => $^=`" This is a "test"'

     This escape is useful mainly for macro packages like `trace.tmac'
     which redefines some requests and macros for debugging purposes.


  Enjoy!


     Werner