Move interpolation_masked_data to utils.interpolation
Add mask_to_mirrored_num
Remove mask_to_mirrored_num from photutils.extern
Update psf photometry to utils.mask_to_mirrored_num
Fix example in mask_to_mirrored_num
Added tests and minor changes to psf.py
Merge pull request #214 from larrybradley/interpolation

Add mask_to_mirrored_num
Merge pull request #216 from adonath/psf_photometry_tests

Added tests and minor changes to psf.py
Followup to #216 for GaussianPSF amplitude
Update tests for GaussianPSF amplitude
Fixing missing coordinate unit in aperture_photometry return for single positions
Merge pull request #213 from bsipocz/aperture_fix_unit_single_position

Fixing missing coordinate unit in aperture_photometry return table
Merge pull request #218 from larrybradley/psf-amplitude

Followup to #216 for GaussianPSF amplitude