1. Fix EXT0 wakeup pin error on ESP32: GPIO3 is not a RTC IO, change to use GPIO25.
2. Add ESP_ERROR_CHECK to explicitly show the runtime error
3. Improve example README
The following commit updates the first half of the the system
example README files. Some other changes were also made:
* Updated base_mac_address example
* Moved contents in GCOV README to GCOV docs
* Some *main.c file names updated
* Updated example README template
The CONFIG_BOOTLOADER_SKIP_VALIDATE_IN_DEEP_SLEEP option is enabled
by default for the following examples:
- system/deep_sleep,
- system/ulp,
- system/ulp_adc.