[dwm] bar toggling

Hi there,

I introduced the new Mod1-b shortcut to dwm, which will be included in
the 4.1 release. This shortcut toggles the status bar on/off.
Also, the config.h define TOPBAR has been replaced by BARPOS
which can be set to BarTop, BarBot, or BarOff by default. I keep
the default setting to BarTop.

So all in all, the new Mod1-b shortcut allows me to use the
whole screen for the windows in use. ;)

Please report any issues you notice with hg tip.

Regards,

-- 
 Anselm R. Garbe >< http://www.suckless.org/ >< GPG key: 0D73F361