Initial fix for issue 2555
Small modifications to enable keyword retrieval
Pass requested keywords as a string.
Allow multiple --key arguments
--keyword instead of --key
--keyword instead of --key
Adds support for the fitsheader --table feature
Adds support for the fitsheader --table feature
Simplified code and improved docstrings
Adds a test for the fitsheader --table feature
improved the usage string and tests
improved the usage strings and tests
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