Donut Charts

This really couldn't be easier. Create a Donut chart using Morris.Donut(options), with the following options.

`data` required	The data to plot. This is an array of objects, containing `label` and `value` attributes corresponding to the labels and sizes of the segments of the donut chart. Note: by default, the segment with the greatest value will be initially selected. You can change the selection using the `select(index)` method on the object returned by `Morris.Donut`. Note 2: as for line charts, if you need to update the plot, use the `setData` method on the object that `Morris.Donut` returns.
`element` required	The ID of (or a reference to) the element into which to insert the graph. Note: this element must have a width and height defined in its styling.
`colors`	An array of strings containing HTML-style hex colors for each of the donut segments. Note: if there are fewer colors than segments, the colors will cycle back to the start of the array when exhausted.
`formatter`	A function that will translate a y-value into a label for the centre of the donut. eg: currency `function (y, data) { return '$' + y }` Note: if required, the method is also passed an optional second argument, which is the complete data row for the given value.
`resize`	Set to `true` to enable automatic resizing when the containing element resizes. (default: false). This has a significant performance impact, so is disabled by default.