Validate time inputs and allow any value that Time accepts
Localize the Time import to _convert_to_time
Fix minor test typo
Merge pull request #18 from taldcroft/coordinates-ape5-times

Validate time inputs and allow any value that Time accepts
change TIME_FRAME_ATTRS to self/class-level time_attr_names
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