add ctrl-e and ctrl-y

Adds support for `ctrl-e` and `ctrl-y`.

![ctrley](https://f.cloud.github.com/assets/942395/2299911/c675461a-a0d8-11e3-8ee8-400838ac0ca0.gif)

As with #77, I haven't added specs because I don't know how to assert the screen is scrolling. If someone can point me in the right direction here I'll gladly write specs.