[SYS/BT] Semaphores and new BT Controller (#1819)

Add semaphore to the enqueue calls to avoid concurrency issues
Add new BT controller to avoid scan evt timeout bug

lib/esp32-bt-lib/README.rst

@@ -0,0 +1,10 @@
+ESP32 BT/BLE Stack Libraries
+====================
+
+This repository contains binary libraries supporting the ESP32 RF subsystems. It is used as a submodule within `Espressif IoT Development Framework`_ (ESP-IDF).
+
+Files in this repository are Copyright (C) 2015-2016 Espressif Systems.
+
+These binary libraries are provided under the same license as the parent esp-idf project - the Apache License 2.0 as provided in the file LICENSE. (The license text refers to this as "Object" form.)
+
+.. _Espressif IoT Development Framework: https://github.com/espressif/esp-idf