Bundle imageutils and update photutils to use latest API
Merge pull request #132 from astrofrog/bundle-imageutils

Bundle imageutils for photutils 0.1 release
Tidy up aperture_funcs.py to avoid duplicated code
Simplify center mode since using subpixel mode with subpixels=1 is actually faster (by at least 50% in some cases)
Remove imageutils from .travis.yml