+ * WindVane sensor. The compass is a number of sectors, 0...(sectors - 1).
+ * sectors must be a power of 2. Sector zero is North, and sectors/2 is South.
+ * Like any compass, the heading increases as one traverses the compass
+ * clockwise. The number of sectors are contrained by the uint8_t data members
+ * of wind_vane_t to 128.