Partially fix Python 3 compatibility
More Python 3 fixes
Updated bundled six to 1.7.3
Revert a few changes
Fixed test errors
Fix compatibility with astropy 1.0.dev
Fix API change in MPL v1.4

Closes #440
Update travis matrix
Fix Sphinx issue
Install more packages with conda instead of pip
Remove pip arguments
Explicitly install coverage with conda
Merge pull request #202 from astrofrog/fix-python3

Implement Python 3 compatibility