Add heatmap support

[sean-]

Are there any plans to implement something like pterm's heatmap (something like pterm/pterm#487)?

[neomantra]

Thanks for that suggestion and reference -- pterm looks like a great library. We intend to add more graph types over time and will consider a heat map implementation. However, there is no immediate plan to add it.

[neomantra]

After some inspiration and sample ideas to base it on, I've released initial heat-map support. Main aspects missing are axis labeling and better UX. It's fresh so please leave any feedback.

• Examples
• heatmap in Go Doc