Add redcarpet.

I propose to add  [redcarpet](https://github.com/vmg/redcarpet) to lokka as markdown parser.

![Screen Shot 2013-01-19 at 10 39 29 PM](https://f.cloud.github.com/assets/1663465/80283/20fd9216-623e-11e2-951e-0a099b218326.png)

![Screen Shot 2013-01-19 at 10 38 16 PM](https://f.cloud.github.com/assets/1663465/80282/0f3a3368-623e-11e2-9b3c-bf6ae1ba4f63.png)