Twit 05 implements an infinite list

Does what it says on the tin :smile: 

![roundandround](https://cloud.githubusercontent.com/assets/3380092/3951658/91bdcee2-26d9-11e4-9b7e-e08b1a8ef48b.gif)

in my head, being `atEnd` means you are 'overHalfWay'