added CMakeLists.txt for use under ESP-IDF

[diplfranzhoepfinger]

see https://docs.espressif.com/projects/arduino-esp32/en/latest/esp-idf_component.html

[RobTillaart]

Interesting addition for a vertical market.
Does not interfere with anything of the code so no risks imho

@diplfranzhoepfinger
Can you add some comments in the file? meta info / header?

Thinking of this.

# Author: diplfranzhoepfinger 
# reference:  https://docs.espressif.com/projects/arduino-esp32/en/latest/esp-idf_component.html
# URL: https://github.com/milesburton/Arduino-Temperature-Control-Library
# DATE: 
...

[RobTillaart]

LGTM

[milesburton]

LGTM

I had to google that Rob!

[diplfranzhoepfinger]

I had to google that Rob!

who is Rob ?

[milesburton]

@diplfranzhoepfinger Ah sorry, I was referring to @RobTillaart and his use of 'LGTM' of which I've never seen before :)