Updated map functions to use physical_constants.h. Also fixed constant
usage in CoordinateConversions.c.
DistanceBetweenLatLng now returns meters, instead of kilometers.
Added DistanceBetweenLatLngAlt method.
Added MapPoint::DistanceToPoint_2D and MapPoint::DistanceToPoint_3D
methods.
Add UAVItem to MapPoint class.
Add GPSItem to MapPoint class.
Renamed class MapItem --> MapPointItem.
Moved type() to parent class.