Parse this comma separated string to find GPIO pins on which we must
enable DHT sensors. Seperators are space and comma.
Can be empty, single GPIO pins, or a list:
app.dht_gpio=""
app.dht_gpio="5"
app.dht_gpio="5,4,14"
app.dht_gpio="5 4 14"
app.dht_gpio="5, 4 14"
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
