Add 3 new styles with color schemes from Tableau

I've taken three color schemes from Tableau Public and ported them into a matplotlib style. I've also added some custom styling that makes the plots look cleaner and clearer by default.

Some things to discuss before merging:

* Given that only the color scheme and not the rest of the styling is from Tableau, should these styles be called "tableau"?

* Should there be separate styles that introduce the color schemes, and then another separate style that introduces my custom stylings?

These styles should result in plots that look similar to this one:

![Example visualization](http://www.randalolson.com/wp-content/uploads/percent-bachelors-degrees-women-usa.png)