Enhance Board MCU information by CPU Revision for boards with ESP32

[cyberman54]

For boards with ESP32 detect CPU Revision (currently Rev.0 and Rev.1) and print it with Board MCU

https://espressif.com/sites/default/files/documentation/eco_and_workarounds_for_bugs_in_esp32_en.pdf

[cyberman54]

See code here

[MattFryer]

Great idea! Currently all the board identification is done at compile time and as this can only be identified at run time on the ESP32, I need to have a think about how best to implement this and maintain the zero/minimum resource usage of the library. Maybe a series of classes, one for each board type with methods to return the possible info? That way no resources will be used unless an instance is created.