Enhancements to AeroVaneReadC.

* Anemometer is read immediately after the Timer fires to reduce jitter.
* Count interface is renamed Revolutions to be more meaningful.
* m_count is now uint8_t to reflect a more reasonable real life range.
* Direction data is returned no as degrees but as a 10-bit unsigned value.
* m_sum accumulates the correct, updated angle values.
* Rounding is done properly when m_sum is negative.