2. added README_flash.txt to folder target/esp32
3. added README_flash.txt to zip file created in $(ESP_ZIP):.... in Makefile
4. added header and source file for PWM. ESP32 does not support a general PWM driver(yet).
Therefore driver/ledc is used.
5 channel can be used for simple DAC, using default frequency of 5000Hz
3 more channel are available for different frequency
5. connect jshardwarePWM functions to standard calls in jshardware
6. implemented jshSetOutputValue in jshardware
7. moved targets/esp32/rtosutil.c from RTOS to standard part of ESP32
targets/esp32/jswrap_rtos.c is added only if var RTOS is defined
