Reorganize stumpwmrc.
Massive teardown and overhaul.

Lots of code that had glommed onto .stumpwmrc is removed (to new packages.)

Stumpwm bindings and commands in other packages now moved to stumpwmrc.

Lots of dead code removed.

Before dropping Stump entirely, I tried to control multi-head behavior...
Unsuccessfully. I think it'd take a bit more XLib knowledge to make it work right,
as OTHER-HEAD-WINDOW et al didn't work.

Patching SLIME-REPL-PREVIOUS-INPUT continues to prove a massive PITA.
Maintaining my own Slime repo would make more sense, maybe.

ERC turns out to be deficient; in a pinch, I couldn't /ban. WTF, ERC.

Radio is ready to be packaged. Its subordinate MPlayer process no longer
opens an output stream, so we don't have to worry about closing it properly.
Only start swank if there's no X server.
Add MONITORS to SBCL startup.