Add support for ESP32

[brentru]

Adds SleepDog support for the ESP32

• Uses the ESP32's as the Watchdog Timer (TWDT) for WDT-support since it can be configured during runtime.
  • Defaults to utilizing the current running task as a subscription for the TWDT.
  • Executes the ESP32's panic-handler TWDT times out
• Adds timer-based low-power-sleep support for ESP32.

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Tested with: Adafruit ESP32 Feather

BasicUsage

11:22:40.250 -> �Watchdog Library Demo!
11:22:40.250 -> 
11:22:40.250 -> Enabled the watchdog with max countdown of 4000 milliseconds!
11:22:40.250 -> 
11:22:40.250 -> Looping ten times while resetting the watchdog...
11:22:40.250 -> Loop #1
11:22:41.264 -> Loop #2
11:22:42.270 -> Loop #3
11:22:43.248 -> Loop #4
11:22:44.262 -> Loop #5
11:22:45.236 -> Loop #6
11:22:46.259 -> Loop #7
11:22:47.239 -> Loop #8
11:22:48.244 -> Loop #9
11:22:49.266 -> Loop #10
11:22:50.251 -> 
11:22:50.251 -> Get ready, the watchdog will reset in 4000 milliseconds!
11:22:50.251 -> 
11:22:54.295 -> E (28103) task_wdt: Task watchdog got triggered. The following tasks did not reset the watchdog in time:
11:22:54.295 -> E (28103) task_wdt:  - loopTask (CPU 1)
11:22:54.295 -> E (28103) task_wdt: Tasks currently running:
11:22:54.295 -> E (28103) task_wdt: CPU 0: IDLE
11:22:54.295 -> E (28103) task_wdt: CPU 1: IDLE
11:22:54.295 -> E (28103) task_wdt: Aborting.
11:22:54.295 -> 
11:22:54.295 -> abort() was called at PC 0x400d5107 on core 0
11:22:54.295 -> 
11:22:54.295 -> 
11:22:54.295 -> Backtrace:0x400d5bc5:0x3ffbe7900x40086f91:0x3ffbe7b0 0x4008bf79:0x3ffbe7d0 0x400d5107:0x3ffbe850 0x40084275:0x3ffbe880 0x400e9f83:0x3ffbd3a0 0x400d5a02:0x3ffbd3c0 0x400882c0:0x3ffbd3e0 
11:22:54.295 -> 
11:22:54.295 -> 
11:22:54.295 -> 
11:22:54.295 -> 
11:22:54.295 -> ELF file SHA256: 0000000000000000
11:22:54.295 -> 
11:22:54.295 -> Rebooting...
11:22:54.332 -> ets Jul 29 2019 12:21:46
11:22:54.332 -> 
11:22:54.332 -> rst:0xc (SW_CPU_RESET),boot:0x13 (SPI_FAST_FLASH_BOOT)
11:22:54.332 -> configsip: 0, SPIWP:0xee
11:22:54.332 -> clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
11:22:54.332 -> mode:DIO, clock div:1
11:22:54.332 -> load:0x3fff0030,len:1252
11:22:54.332 -> load:0x40078000,len:12732
11:22:54.332 -> load:0x40080400,len:3100
11:22:54.332 -> entry 0x400805ec
11:22:54.436 -> Adafruit Watchdog Library Demo!

Sleep

11:23:49.026 -> Watchdog Library Sleep Demo!
11:23:49.026 -> 
11:23:49.026 -> Going to sleep in one second...
11:23:51.033 -> I'm awake now! I slept for 1000 milliseconds.