make get_transform always return a CompositeTransform
Initial commit of SkyCoordinate high-level class
Use BaseCoordinateFrame not SphericalCoordinatesBase
Change SkyCoordinate to SkyCoord
Update to use frame_transform_graph
Change COORD to FRAME for globals names
Factor out  determination and allow specification in args
Major refactor of input args, kwargs processing
Restrict transform_to system to be a string and do transform correctly
Change  to  everywhere
Update repr to match low-level class repr more closely
Add support for two positional args
Add initial SkyCoord API tests
Allow for frame class as initializer for frame
Improve and generalize frame attribute handling
Work on inheritance of attributes during initialization
Check that existing valid kwarg is not None for conflict resolution
Improve attribute conflict resolution and add tests
Allow for Representation instances to init SkyCoord
Add bunch of tests