Add ability to work along axis for sigma_clip
Add ability to work along axis for sigma_clip
Add ability to work along axis for sigma_clip
Add ability to work along axis for sigma_clip
Merge branch 'sigma-clip-by-axis' of github.com:mhvk/astropy into sigma-clip-by-axis
Second iteration of allow sigma clip by axis.
Replaced maout with copy and simplified, following suggestion of @astrofrog.