Better color scaling

[piegamesde]

As with on GitHub, the colors in the charts have two major issues:

• The scale is not logarithmic, so that a couple of days with a lot of activity easily dwarf the rest of the chart
• The scale is not the same across years, so it is difficult to read long-term trends across years.

I think both could be fixed simultaneously.

[sallar]

the goal of this project is to exactly replicate how github works... so we dont do any calculation for the scale in this project. I don't know if we should or not.