Allow a mouse binding to hide a window, and add a default keybinding for CMS-M3,

so it's hard to press by accident, but there if you need it.

requested (in a way) and tested by johan and todd.

cwmrc.5

@@ -314,6 +314,8 @@ move a window
 resize a window
 .It window_lower
 lower a window
+.It window_hide
+hide a window
 .It window_grouptoggle
 toggle group membership of a window
 .It menu_group