…olormesh.

- Allows for percent or raw count representation of the predictions
- Implements heatmap with white=0, green=100%, and yellow-orange-red heatmap for everything else
- Allows zooming in on confusion matrix using passed list of classes, with accurate %-of-all-true calculations
- Tested for moderately large class numbers (30+)
- Diagonal line indicates accurate predictions
- Documentation added to docs/examples/methods.rst for one example matrix

Suggested future improvements:
- Resize font based on image size + class count
- Allow custom color coding, including custom colors for _over and _under values (e.g. zero and 100%)
- Vary text font color based on background color
- While this branch currently adds an example to methods.rst, the examples/confusionMatrix.ipynb has additional examples using different of the passed parameters. This should probably also be exported as rst and added to the docs, but there was not an obvious place to put it so I am excluding that for now.

Note this commit squashes all previous commits on this branch

# Conflicts:
#	examples/nealhumphrey/confusionMatrix.ipynb
#	yellowbrick/classifier.py
#	yellowbrick/utils.py

… notebooks to make sure they work.