initial checkin of new approach
just use subtracted angle
screwed up relative imports
oops, had double units on roll angle
 update docstring
added galactocentric import to init
added tests for galactocentric
added a todo about #3217
update docstring to explain ICRS and roll angle
change definition of roll angle to be deviation from Galactic xz plane
added Galactocentric to list of frames in init
typo in comment - transforming from ICRS not galactic
remove extraneous xyz definition
change random to linspace, fix typo with roll angle (which caused build failures)
enforced 75 char limit in docstring
clarified position of the sun [ci skip]
fixed up quantity to get coordinate docs to build
decompose height/distance calculation to avoid weird Quantity behavior reported in #3240
fixed support for Nd arrays, added tests
remove TODO comment [ci skip]