ESP32: Bluetooth tutorials with BTStack library

[anteph]

Some tutorials on getting started with Bluetooth on the ESP32, using IDF and the BTStack library.

Bluetooth Classic:
- Using the BTStack library: https://techtutorialsx.com/2017/07/08/e ... k-library/
- Finding a ESP32 Bluetooth device with Python: https://techtutorialsx.com/2017/07/09/e ... d-btstack/
- Receiving data on the ESP32 through RFCOMM: https://techtutorialsx.com/2017/07/09/e ... th-rfcomm/
- Advertising a SPP service with SDP : https://techtutorialsx.com/2017/07/17/e ... -with-sdp/