AP_HAL: added voltage_average() interface to AnalogIn

returns voltage in Volts, using averaged reading over samples.

Where possible this should be auto-scaled against a known reference
voltage
AP_ADC_AnalogSource: added voltage_average() interface
Plane: use voltage_average() to not depend on INPUT_VOLTS
Copter: use voltage_average() so as to avoid INPUT_VOLTS
Rover: use voltage_average() interface
HAL_AVR_SITL: fixed windows build
build: fixed cygwin build
Compass: current based compensation added
Copter: add current based compass compensation
Copter: remove unused input_voltage parameter
Copter: use unsigned long for dataflash log for gps time

Updated some formatting of comments in the same file
Copter: minor formatting fix for report_ins
TradHeli: remove duplicate RC_FAST_SPEED definition
Copter: only start delay timer after reaching wp location and altitude
AP_ADC: fixed scaling factor for voltage on APM1 Ch6 ADC
AP_Rangefinder: use voltage_average() interface for generic analog rangefinder
AP_ADC_AnalogSource: fixed reference scaling for APM1 Ch6 ADC

it is not referenced to Vcc
AP_Airspeed: use new voltage_average() API in Airspeed driver
Plane: removed INPUT_VOLTS parameter

no longer needed
Rover: removed INPUT_VOLTS parameter

no longer needed