Feature Request : Multiple scales

[guspower]

Thank You

Firstly thank you for a beautiful library - elm-charts is a joy to use.

Overview

I have a number of business scenarios where I would like to plot two different types of data on the same graph to more obviously show correlation between different data series.

Sample Scenario

Show user acquisition (number of users per unit time) and revenue earned (money per unit time) together on the same graph. This would require having two y axes, one displaying the units for the one series (or set of series) and the other displaying the units for the other series (or set).

Contributing

I read on the administration page that this feature has been mentioned as part of upcoming features. I am happy to contribute in whatever way I can (code, testing etc.) if one or more of the maintainers are interested in this enhancement.