Rover: added compass logging
Plane: added compass logging
Plane: when logging is disabled don't include DataFlash at all
Rover: cleanup build warnings
AP_Math: move print_latlon() to location.cpp
DataFlash: use print_latlon()
Rover: log board voltage
Plane: log board voltage
Plane: log parameter changes
Copter: convert to new logging system
DataFlash: simplify code now that copter is converted

no longer need as many public functions
DataFlash: convert example sketch to new API
Copter: added board voltage to current message
DataFlash_File: fixed creation of 0.log
Copter: removed duplicate print_latlon() declarations
AP_GPS: removed duplicate print_latlon()
DataFlash: added support for printing flight mode as a string

makes analysing logs easier.

Pair-Programmed-With: Randy
Plane: print flight mode as string in logs
Copter: print flight mode as string
Rover: print mode as string in logs