all using US frequencies. This build fixes this (and makes the build
system cleaner in general).
If you are building your own builds in the IDE you'll need to start
setting an environment variable called COUNTRY to your two letter
country code (or leave unset to get US frequencies). See new comment
in platformio.ini.
* preflightSleep, notifySleep, notifyDeepSleep now allow arbitrary
drivers/devices/software to register for sleep notification.
* Use the proceeding to clean up MeshRadio - now the mesh radio is more
like an independent driver that doesn't care so much about other systems
* clean up MeshService so that it can work with zero MeshRadios added.
This is a prelude to supporting boards with multiple interfaces (wifi,
extra LORA radios etc) and allows development/testing in sim with a bare
ESP32 board
* Remove remaining ESP32 dependencies from the bare simulation target
this allows running on anything that implements the arduino API
* to allow changing to new mesh transport
* to allow a different chipset for the radio
* to allow testing on hardware with a SimRadio
* new "bare" build env for a devboard with virtually no hardware
* make buttons optional
