Very rough stab just to test the waters -- this will need some
more work.
For now, hard code 4,5,15 pins (as per Sonoff SV), but before
rolling this out, add a config flag for this behavior.
Neat trick -- the presence of dht library in mos.yml triggers
inclusion of the code via define -DMGOS_HAVE_DHT=1
- Refactor mqtt_publish_stat() to take va_list
- Make publish_stat format its response with json_vprintf() so it is
valid JSON.
- Call publish_stat in channel_set, the only place where the GPIO state
changes
- Return (valid) JSON response in all RPCs