Initial version of rmt driver (espressif#1525)

* rmt driver initial version

* supporting conti mode plus interrupts

* using conitnous mode for sending more data

* working continous mode

* rmt driver cleanup after conti mode

* initial version of rmt driver

* adding a simple example

* adding channel and block locks

* modified of rmt interface for simpler/easier usage

* adding header sentinels, split interface to common and additional settings

* Fixes per code review + support for rx callback mode

* renamed internal structures and enums, fixed formatting

* cmake support for rmt

* refactored tx-conti interrupts to function to make it more readable

* added Tx and Rx examples

* added license headers

* minor updates per review

* used struct access, renamed defines, corrected diagram

Author: david-cermak

CMakeLists.txt

@@ -16,6 +16,7 @@ set(CORE_SRCS
   cores/esp32/esp32-hal-timer.c
   cores/esp32/esp32-hal-touch.c
   cores/esp32/esp32-hal-uart.c
+  cores/esp32/esp32-hal-rmt.c
   cores/esp32/Esp.cpp
   cores/esp32/FunctionalInterrupt.cpp
   cores/esp32/HardwareSerial.cpp