Implemented multi-dimensional filtering for heat maps

- filter handling now accepts arrays as filter keys.
- brush filters no longer use arrays, but the RangedFilter utility
Adding example for heatmap filtering across multiple charts

Fixed bug where bar chart wouldn't update colors on rerender
Fixed a bug where zooming would lose the RangeFilter functionality
Fixed issue with web renderer test
Added heatmap row and column filtering.
Converted heatmap tests to jasmine
Fixed bug where heatmap filtering would rely on array equality
Expanded heatmap examples to drive out support for multiple datapoints behind a two-dimensional value

Added configurable border radius to heatmap tiles
Merge pull request #407

Conflicts:
	spec/helpers/fixtures.js
	src/heatmap.js