Multiple y-axis for stacked column chart
Currently, if you use multiple Y-axis in combination with a stacked column chart, all columns are stacked together. Example:
I propose that only the columns belonging to the same y-axis are stacked together. This would mean that in the example above, "Rainfall 3" would not be stacked on top of the others, but rendered next to it and have it's own axis.
If there was an additional series with y-axis=1 would be rendered on top of "Rainfall 3"
You can achieve that by giving the series a separate stack option. For simplicity you can call it the same as the yAxis option: http://jsfiddle.net/Lanerxnr/3/.