[wrt] Add liblmfit-lua based on lmfit-2.4
[lm] Add curve fitting to linkmeterd for unknown probe calculation

$LMUP,command
start - Switch Pit to Celcius and probes to resistance
fit - Return the JSON-formatted steinhart curve fit of the current Food1 probe
csv - Return the csv-formatted data of temperature,resistance
stop - Stop unknown probe calculation and return to normal temperature units
[wrt] Include liblmfit-lua in BCM2708 target