Add FromDegrees methods for other types

[airbreather]

The change to make Angle's constructors all private means that creating other types composed of Angles is now more verbose. e.g.: var c = new GlobalCoordinates(Angle.FromDegrees(38.88922), Angle.FromDegrees(-77.04978));

A friendlier alternative to that might look like: var c = GlobalCoordinates.FromDegreesLatitudeAndLongitude(38.88922, -77.04978);