[AnalogSensors] updated HMC6352PseudoAnalogSensor code

- behavior is now fully implemented and allows to read heading
[AnalogSensors] cleaned up AD7995AnalogTODigitalconverter class

- made the code look a little bit more like other ones (MCP3428, ...)
[AnalogSensors] cleaned up (minor changes) AnalogSensors API
[AnalogSensors] cleaned up (minor changes) BuiltInAnalogSensor API
[AnalogSensors] detailed comment in AnalogSensors API
[AnalogSensors] changed ADC implementation behaviour

- now ADC implementations return 0 when read fails
[AnalogSensors] Fixed syntax errors un AD7995AnalogToDigitalConverter

- previous commit was a little bit optimistic, and lacked rebuild ...
;-)