HEADS UP: change key binding for swapLeft/Right and IncMaster

The use of arrow keys for swapLeft/Right clash with firefox's back
button. Use the more intuitive mod-shift-jk for this. (It's a movement
operation, after all).

This clashes with IncMaster, so we use mod+comma and mod+period for
these (i.e. the keys mod < and mod > , to move windows to and from the
master area).

While we're here, replace the use of the terms 'left' and 'right' for
navigation, in comments and identifiers, with 'up' and 'down' instead.
Hence mod-j == focusDown. Far more intuitive for people (dons) who live
in fullscreen mode and have vim movement wired into their central
nervous system.

Principle of least VI surprise: movement down or up means using j and k.

Config.hs

@@ -148,35 +148,40 @@ defaultLayouts = [ full
 --
 keys :: M.Map (KeyMask, KeySym) (X ())
 keys = M.fromList $
+    -- launching and killing programs
     [ ((modMask .|. shiftMask, xK_Return), spawn "xterm")
     , ((modMask,               xK_p     ), spawn "exe=`dmenu_path | dmenu` && exec $exe")
     , ((modMask .|. shiftMask, xK_p     ), spawn "gmrun")
+    , ((modMask .|. shiftMask, xK_c     ), kill)
+
+    -- rotate through the available layout algorithms
     , ((modMask,               xK_space ), switchLayout)
 
     -- 'nudge': resize viewed windows to the correct size.
     , ((modMask,               xK_n     ), refresh)
 
-    , ((modMask,               xK_Tab   ), focusRight)
-    , ((modMask,               xK_j     ), focusRight)
-    , ((modMask,               xK_k     ), focusLeft)
+    -- move focus up or down the window stack
+    , ((modMask,               xK_Tab   ), focusDown)
+    , ((modMask,               xK_j     ), focusDown)
+    , ((modMask,               xK_k     ), focusUp)
 
-    , ((modMask,               xK_Left  ), swapLeft)
-    , ((modMask,               xK_Right ), swapRight)
+    -- modifying the window order
+    , ((modMask,               xK_Return), swapMaster)
+    , ((modMask .|. shiftMask, xK_j     ), swapDown)
+    , ((modMask .|. shiftMask, xK_k     ), swapUp)
 
+    -- resizing the master/slave ratio
     , ((modMask,               xK_h     ), sendMessage Shrink)
     , ((modMask,               xK_l     ), sendMessage Expand)
 
-    , ((modMask .|. shiftMask, xK_j     ), sendMessage (IncMasterN 1))
-    , ((modMask .|. shiftMask, xK_k     ), sendMessage (IncMasterN (-1)))
-
-    , ((modMask .|. shiftMask, xK_c     ), kill)
+    -- increase or decrease number of windows in the master area
+    , ((modMask              , xK_comma ), sendMessage (IncMasterN 1))
+    , ((modMask              , xK_period), sendMessage (IncMasterN (-1)))
 
+    -- quit, or restart
     , ((modMask .|. shiftMask, xK_q                     ), io $ exitWith ExitSuccess)
     , ((modMask .|. shiftMask .|. controlMask, xK_q     ), restart Nothing True)
 
-    -- Cycle the current tiling order
-    , ((modMask,               xK_Return), swapMaster)
-
     ] ++
     -- Keybindings to get to each workspace:
     [((m .|. modMask, k), f i)