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
Updated Miniconda to 3.6.0
Merge pull request #443 from astrofrog/update-miniconda

Updated miniconda and install a few more packages using conda instead of pip
Custom viewer
Better binning of categorical histograms
More progress and documentation on custom viewers
Custom widgets. Documentation + bball example
use six