Calendar heatmap in plain Go inspired by Github contribution activity visualization.

Colorscales
![PuBu9](example/chart_PuBu9.png)
![GnBu9](example/chart_GnBu9.png)
![YlGn9](example/chart_YlGn9.png)

Without month separator
![PuBu9_noseparator](example/chart_PuBu9_noseparator.png)

You can run it in your Go code or as standalone script. 
Check `example/main.go` and `input.txt` for more details.