Used the Bar chart as a starting point for heatmap.
Completed a simple HeatMap implementation. Also added examples.
Made the color mapper more generic.
Now supporting palettes.
Avoid grids in some categorical charts.
Removed checkpoint folder.
Change names and fixed examples.
Added HoverTool.
Merge master-in, fixed conflicts.
Merge master-in again, fixed conflicts.
Fixed tests.
Merge pull request #1126 from ContinuumIO/feature/heatmap

Feature/heatmap