feat(event) rework the prototype of lv_event_cb

It encapsulates all event related parameters into a single lv_event_t obejct.

docs/get-started/quick-overview.md

@@ -117,7 +117,7 @@ lv_obj_set_event_cb(btn, btn_event_cb);                 /*Assign a callback to t
 
 void btn_event_cb(lv_obj_t * btn, lv_event_t event)
 {
-    if(event == LV_EVENT_CLICKED) {
+    if(code == LV_EVENT_CLICKED) {
         printf("Clicked\n");
     }
 }

docs/overview/event.md

@@ -176,7 +176,7 @@ There are 2 custom pointer that are available in the events:
 - `user_data`: set when the event is registered. 
 - `event_param`: set when the event is sent in `lv_event_send`
 
-In any event callback these pointer can be get with `lv_event_get_user_data()` and `lv_event_get_param()`.
+In any event callback these pointer can be get with `lv_event_get_user_data(e)` and `lv_event_get_param(e)`.
 
 
 ## Event bubbling