TODO

Features
- Filter for group values by regex
- Filter cohorts by start/end
- Negative axis for negative values; move axis to top and have values go down
- Combine positive/negative stacked bar charts by putting the delta between positive and negative in the stack above or below; indicate the zero point with a thick line; make the line red when it's negative, black when it's positive.
- Click on a bar segment to make that location stick, so all calculations remain frozen until the user clicks on it again or on another square.

Help
- Other datasets (funnel, retention, sales) that can be loaded as examples with a single click; preconfigures the view settings.
- Help manual that explains common operations, screenshots of the visualizations they generate.

Bugs
- X axis is truncated at the last label; it should keep going to the end