Update astropy_helpers version
Merge pull request #182 from crawfordsm/fits_adu

Added catch if adu is uppercase in fits header
Merge pull request #178 from heidtna/line78

Added dtype argument to combiner
Merge pull request #181 from crawfordsm/changelog

I'll go ahead and merge, then we can do additions to README and docs separately. Will open issues for those.
Update CHANGES.rst