Feature: implement mouse bindings

A configured mouse binding (for example `bindsym button3 kill`) runs
its command when the mouse button is pressed over parts of a container.

If the binding has no modifer, it will only run when the button is
clicked on the window titlebar.

Otherwise if the binding has a modifier, it will run over the titlebar
or any part of the contained window.

fixes #558

src/click.c

@@ -177,6 +177,29 @@ static int route_click(Con *con, xcb_button_press_event_t *event, const bool mod
     if (con->parent->type == CT_DOCKAREA)
         goto done;
 
+    /* if the user has bound an action to this click, it should override the
+     * default behavior. */
+    if (dest == CLICK_DECORATION || dest == CLICK_INSIDE) {
+        Binding *bind = get_binding_from_xcb_event((xcb_generic_event_t *)event);
+        /* clicks over a window decoration will always trigger the binding and
+         * clicks on the inside of the window will only trigger a binding if it
+         * has modifiers. */
+        if (bind && (dest == CLICK_DECORATION || (bind->mods && dest == CLICK_INSIDE))) {
+            CommandResult *result = run_binding(bind, con);
+
+            /* ASYNC_POINTER eats the event */
+            xcb_allow_events(conn, XCB_ALLOW_ASYNC_POINTER, event->time);
+            xcb_flush(conn);
+
+            if (result->needs_tree_render)
+                tree_render();
+
+            command_result_free(result);
+
+            return 0;
+        }
+    }
+
     /* Any click in a workspace should focus that workspace. If the
      * workspace is on another output we need to do a workspace_show in
      * order for i3bar (and others) to notice the change in workspace. */
@@ -300,6 +323,7 @@ done:
     xcb_allow_events(conn, XCB_ALLOW_REPLAY_POINTER, event->time);
     xcb_flush(conn);
     tree_render();
+
     return 0;
 }