Mark tests that require scikit-image
Merge pull request #78 from cdeil/skimage_skip_tests

Mark tests that require scikit-image
WIP: Adding list of position (x,y) tuples to CircularAperture
WIP: corner positions work with CircularAperture
Clean up, and adding back masking to aperture_photomery and some checks in CircularAperture
WIP: Changing tests due to api change
Adding position to CircularAnnulus
Adding position to EllipticalAperture
Adding position to EllipticalAnnulus
Adding position to RectangularAperture
Modifying benchmark
Removing unnecessary loop
Removing loop bug
Removing unnecessary loop from non-circular apertures
Fixing error not None case
Changing test_apertures to address coordinate addition to aperture objects
Adding aperture_photometry tests back, and enhance method coverage
Adding test for RectangularAperture
Remove unnecessary returns, and cleanup test