coin flip sequences

Eater-

I've done a style + refactor pass on David Sissitka's "coin flip sequences" exercise for Brit, you are more than welcome to modify as you feel appropriate. I added highcharts.js to /utils, it can certainly pull from elsewhere if appropriate.

It looks like the earlier "dice probability" items are also included in this pull request, those should be ignored -- sorry for the noise.

Kitt