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
Warn on invalid WCS unit
CHANGES entry
update setup_helpers and a corresponding setup.py change
Clarify what is returned
Add mad_std function
Add fwhm_to_sigma and sigma_to_fwhm functions
Implement @embray's comments
Prepend "gaussian_" to FWHM <-> sigma conversion functions
Added instructions on setting up affiliated package manually
Added section on updating for manual set-up
Added instructions on updating astropy-helpers
Mention ah_bootstrap.py
Implemented comments by @cdeil
Javascript magic to allow user to specify package name