integrate and link lib curl for android, add VAO support for brush draw, sync canvas with screen redraw instead of input events

android/src/main/cpp/main.cpp

@@ -257,6 +257,7 @@ static void engine_handle_cmd(struct android_app* app, int32_t cmd) {
         case APP_CMD_TERM_WINDOW:
             // The window is being hidden or closed, clean it up.
             engine_term_display(engine);
+            exit(0);
             break;
         case APP_CMD_GAINED_FOCUS:
             // When our app gains focus, we start monitoring the accelerometer.
@@ -326,7 +327,7 @@ void android_main(struct android_app* state) {
     app_dummy();
 
     LOG("NETWORK TESTING...");
-    curl_test();
+    //curl_test();
     LOG("NETWORK TESTED");
 
     memset(&engine, 0, sizeof(engine));