Updated temperature sensing code.

Temperature sensor using the MCU ADC subsystem works OK.
Positive and negative temperatures work within tolerance and indicate correctly within AT&T=RSSI.
MAX_PA_TEMP at 70 Deg is a reasonable limit based on actual temperatures, Heatsink temps track within 5 degrees at high temp.
I have reduced the RX buffer to 1024 for development, this is intended only to be temporary.