wmaker: add directional window focus

This patch is adding directional window focus
(like in openbox), where the focus can be passed to
the current window neighboors with a shortcut key.
Comparisons are performed using window centres.

New options are FocusWindowLeftKey, FocusWindowRightKey,
FocusWindowUpKey, FocusWindowDownKey.
Other WM are setting those to SUPER+LEFT/RIGHT/UP/DOWN keys
but currently those are not set by default.

CirculateRaise option which is described in WPrefs as
'Raise window when switching focus with keyboard' is also
used to raise/not raise windows that are fully covered by
other windows.

src/actions.h

@@ -41,6 +41,7 @@
 #define SAVE_GEOMETRY_ALL      SAVE_GEOMETRY_X | SAVE_GEOMETRY_Y | SAVE_GEOMETRY_WIDTH | SAVE_GEOMETRY_HEIGHT
 
 void wSetFocusTo(WScreen *scr, WWindow *wwin);
+void wSetFocusToDirection(WScreen *scr, int direction);
 
 int wMouseMoveWindow(WWindow *wwin, XEvent *ev);
 int wKeyboardMoveResizeWindow(WWindow *wwin);