modules: new HAL layer for esp32

see libraries/AP_HAL_ESP32/README.md for more.

Author: Charles Villard <charlesvillard10@gmail.com>
Author: Buzz <davidbuzz@gmail.com>

.gitmodules

@@ -31,7 +31,9 @@
 [submodule "modules/DroneCAN/DSDL"]
 	path = modules/DroneCAN/DSDL
 	url = git://github.com/DroneCAN/DSDL.git
-
 [submodule "modules/CrashDebug"]
 	path = modules/CrashDebug
 	url = https://github.com/adamgreen/CrashDebug
+[submodule "modules/esp_idf"]
+	path = modules/esp_idf
+	url = git://github.com/espressif/esp-idf.git

README.md

@@ -157,3 +157,7 @@ for reviewing patches on their specific area.
   - ***Subsystem***: OSD
 - [Rishabh Singh ](https://github.com/rishabsingh3003):
   - ***Subsystem***: Avoidance/Proximity
+- [David Bussenschutt ](https://github.com/davidbuzz):
+  - ***Subsystem***: ESP32,AP_HAL_ESP32
+- [Charles Villard ](https://github.com/Silvanosky):
+  - ***Subsystem***: ESP32,AP_HAL_ESP32