Make split between local and nonlocal wcs classes clearer, and add a few classes to make this work correctly
(#364)
Add some more useful functionality to the Angle and CelestialCoord classes
(#364)
Minor edit to where draw calculates the local jacobian.  Use offset to get a better position of the object.
(#364)
Add RaDecFunction and more unit tests of celestial WCS types
(#364)
Use same trick I used for test_tags in other places where we don't want to run all test in normal unit test runs
(#364)
Move bounds shifting ops to python layer
(#364)
Make im.shift, im.setOrigin and im.setCenter update the wcs correctly as well.
(#364)