New option to raise a client via the mouse (unbound by default);

opposing action, lower, already exists and bound.  Both keyboard
mappings already exist.

'no opinion either way' oga@

mousefunc.c

@@ -196,6 +196,12 @@ mousefunc_window_lower(struct client_ctx *cc, void *arg)
 	client_lower(cc);
 }
 
+void
+mousefunc_window_raise(struct client_ctx *cc, void *arg)
+{
+	client_raise(cc);
+}
+
 void
 mousefunc_window_hide(struct client_ctx *cc, void *arg)
 {