Smell driver

The smell code just runs directly on controllers (Feather M0) – the code for the controllers can be found at: https://github.com/tlodge/fmundane-arduino/blob/main/smell/air_freshner_v3.ino

To smell controllers can be called as follows:

endpoint	method	description	params
/on1	GET	Set smell fan on at low speed
/on1	GET	Set smell fan on at medium speed
/on1	GET	Set smell fan on at high speed
/off	GET	Turn off the fan