Scientific number formatting for X Axis?

Hi,

I have noticed that there is no way to have xAxis values formatted as 10^x (.scientific). The only xAxis formatter is of type IAxisValueFormatter and automatically uses stringForValue function. However, this would be a great feature. Could you add it?

Start by tracing the xAxis formatter interface, IAxisValueFormatter, and its stringForValue function. Determine where axis values are formatted and what scientific notation behavior the feature should expose; done means xAxis values can be displayed in scientific notation without breaking existing formatting.

Written by the indexing model from the issue text.