emms-setup-discover

I've pushed `emms-setup-discover' to emms-setup.el and updated the
manual. It interactively looks for players and info methods on the
user's machine and outputs the relevant setup lines.

It's goal is to be another step in easing Emms setup, since when I help
people on IRC with Emms setup the value of
emms-player-list/emms-info-functions is often the culprit.

Perhaps we'll run something like it automatically when Emms is installed
for the first time.

Tell me what you think.

-- 
   "Cut your own wood and it will warm you twice"