add intermediate frames
Add intermediate frames to __init__
ICRS<->CIRS transforms and CIRS self-transform
Remove unneeded import in baseframe
Remove unneeded/confusing return sections in docs
Implement GCRS stuff
initial framework for the cirs<->obs stuff
Change to QuantityFrameAttribute from separate pos and vel
fix typo in QuantityFrameAttribute
working ICRS->AltAz
added get_sun
tentative support for vector time frame attributes
add get_sun tests
added altaz->CIRS transform and AltAz self-transform
added test_cirs_to_altaz and related fix
Minor tweaks in test_transformations
error message typo fix
fix unit typo
add transform full stack tests
added test of full-stack conversion