wmaker: Add option for window snap to top edge to maximize to full screen.

This is a common behavior in a number of other environments, e.g., Unity
and Windows.

WPrefs.app/Expert.c

@@ -97,6 +97,9 @@ static const struct {
 	{ N_("Distance from corner to begin window snap."),
 	  /* default: */ 10, OPTION_WMAKER_INT, "SnapCornerDetect" },
 
+	{ N_("Snapping a window to the top maximizes it to the full screen."),
+	  /* default: */ False, OPTION_WMAKER, "SnapToTopMaximizesFullscreen" },
+
 	{ N_("Open dialogs in the same workspace as their owners."),
 	  /* default: */ False, OPTION_WMAKER, "OpenTransientOnOwnerWorkspace" }