Fixed a dumb bug.
Cleaned up code and added validation.
Merge branch 'master' of github.com:EmitCode/NGps

Conflicts:
	NGps/GpggaReceivedEventArgs.cs
	NGps/GpgsaReceivedEventArgs.cs
	NGps/GprmcReceivedEventArgs.cs
	NGps/GpvtgReceivedEventArgs.cs