Due to the way the headers are organized a single change in a
AP_GPS backend would trigger a rebuild for most of the files in the
project. Time could be saved by using ccache (since most of the things
didn't change) but we can do better, i.e. re-organize
the headers so we don't have to re-build everything.
This makes internal headers internal and then other libraries only
depend on the AP_GPS.h header.
murata
Mathieu OTHACEHE
Andrew Tridgell
Lucas De Marchi
Michael Oborne