Implemented option allowing to specify Donut segment color in data parameter

[stlk]

Hi,
I'm displaying categories with specific color, so I needed way to tell Morris color of each segment. To set segment color just add field called color to data item.

I believe this might be useful to someone else as well.

JSbin: http://jsbin.com/UcUBApA/3/

Example:

Morris.Donut({
    element: 'donut-example',
    data: [
      {
          label: "Download Sales",
          value: 12,
          color: "#5a3163"
      },
      {
          label: "In-Store Sales",
          value: 30,
          color: "#894a96"
      },
      {
          label: "Mail-Order Sales",
          value: 20,
          color: "#ae73ba"
      }
    ]
});

[oesmith]

Great work, thanks! Could you also write some docs for your changes?

Thanks again 👍

[stlk]

I'm happy to see that you found this little addition useful.
As this was my first contribution, I'm not sure what do you mean. Should I update gh-pages branch or just add example to /examples?

Thanks