Lua manual pages

[Marc Balmer <marc%msys.ch@localhost>]

I just committed a man page gpio(3l) that documents the Lua binding to
access gpio(4) pins.  Since this is the first man page that describes a
Lua binding, and more have to come, I would be happy for some feedback
from Lua users.  Is the format useful or does it lack important information?

(Note that you have to update your system _and_ /etc/man.conf to be able
to view Lua man pages).