Add Pie Charts!

[sheweichun]

Explanation About What Code Achieves:

• I add pie chart , you can see it in the demo, I add a pie demo in the create chart section

Steps To Test:

• you can see it in the create chart section

TODOs:

• None
  support label showing in the pie chart
  support annular pie chart

[pratu16x7]

Thanks so much for this! 🎉 (Meanwhile, have updated PR guidelines to include screenshots as well.) Will put one here for all to see:

We were all for percentage charts, as they are easier to read and don't clump colors (probably the reason GitHub ignores them as well): http://www.storytellingwithdata.com/blog/2011/07/death-to-pie-charts

Even so, what does everyone think? 😃

[achillesrasquinha]

Even I prefer percentages over pies, this does not much harm with the tooltip on. I'd pass.

[sheweichun]

after you show the screenshot, I found some thing wrong with the hover effect,it has some deviation,I fix it in my local repository

[pratu16x7]

Cool! Be sure to rebase your branch as well :)