`microcontroller.cpu.temperature` uses different ADC settings, and caused
AnalogIn to give wrong answers. AnalogIn can no longer assume it's the
only user of the ADC.
* Add microcontroller.cpu, the sole instance of microcontroller.Processor.
microcontroller.cpu.frequency is the clock frequency, in Hz.
microcontroller.cpu.temperature is the reading from the internal temperature sensor, in Celsius. None if not available.
* Squeeze firmware size by using -finline-limit. Otherwise non-Express builds were slightly too big.
* Update submodules.
* Fix documentation glitches
