Merge branch 'feature/btdm_common_api' into 'master'

component/bt : add bt device api

1. add get bd_addr function

later, will add other functions reference with bluetooth device.

See merge request !380

docs/api/bt_common.rst

@@ -6,3 +6,4 @@ BT COMMON
 
    Bluetooth DEFINE <esp_bt_defs>
    Bluetooth MAIN <esp_bt_main>
+   Bluetooth DEVICE <esp_bt_device>

docs/api/esp_bt_device.rst

@@ -0,0 +1,48 @@
+BT DEVICE APIs
+===============
+
+Overview
+--------
+
+Bluetooth device reference APIs.
+
+`Instructions`_
+
+Application Example
+-------------------
+
+`Instructions`_
+
+.. _Instructions: template.html
+
+
+API Reference
+-------------
+
+Header Files
+^^^^^^^^^^^^
+
+  * `bt/bluedroid/api/include/esp_bt_device.h <https://github.com/espressif/esp-idf/blob/master/components/bt/bluedroid/api/include/esp_bt_device.h>`_
+
+
+Macros
+^^^^^^
+
+
+Type Definitions
+^^^^^^^^^^^^^^^^
+
+
+Enumerations
+^^^^^^^^^^^^
+
+
+Structures
+^^^^^^^^^^
+
+
+Functions
+^^^^^^^^^
+
+.. doxygenfunction:: esp_bt_dev_get_address
+