[Groff] changing groff_lilypond to glilypond

[Bernd Warken]

I'm about to change the name of `groff_lilypond' to `glilypond'.
That suits better to other `groff' preprocessors.

I could not find this new term in the internet.  So the renaming
seems to do no harm to anyone.

Are there any concerns about the new name?

I rewrote the code to better Perl style.  The handling of temporary
files and directories must still be changed for security reasons. 

Bernd Warken