PEP8 fixes
Small fix
Merge pull request #85 from bsipocz/pep8

PEP8 fixes
Add photutils.datasets sub-package
Add fermi_counts.fits.gz example image file
Add datasets sub-package to docs
Various improvements to datasets code and docs
Add position and amplitude as GaussianPSF constructor parameters
Implement photutils.datasets.make_gaussian_image
Plot each example image in the docs
Mark test_make_gaussian_image as requiring scipy
Use Astropy dev version intersphinx_mapping
Include source in datasets examples