Add .cache to .gitignore
Copy photutils.utils functions
Update imports for new functions
Replace fix_prf_nan with mask_to_mirrored_num
Add tests for mask_to_mirrored_num
Add mask_to_mirrored_num to __all__
Update mask_to_mirrored_sum docs
Add example for mask_to_mirrored_num
Add section on related Astropy packages to the docs
Merge pull request #10 from cdeil/issue-10

State clearly where the boundaries are btwn photutils and imageutils
Merge pull request #11 from larrybradley/photutils

Add photutils.utils functions
added pip requirements file for RTD
another attempt to get the RTD requirements to work right