Added a Readline Cheat Sheet Goodie.

I modeled this off the Vim Cheat Sheet solution.  

DuckDuckHack idea: https://duck.co/ideas/idea/673/cheatsheet-for-readline-keyboard-shortcuts
Data source: http://readline.kablamo.org/emacs.html and http://readline.kablamo.org/vi.html

I have tests and metadata.
I have tested my solution on Ubuntu using Chrome and Firefox.

![image](https://f.cloud.github.com/assets/104742/2364547/0088b726-a67c-11e3-8a0d-dc2022210dbe.png)