Add `figlet` command line interface

I thought it would be cool to have a command line interface to figlet. What do you think?

Use `npm link` to globally symlink the `figlet` command. Otherwise you'll need to use `node bin/cmd.js`

```
$ npm link
$ figlet -f Rectangles "Pull Request?"
                                              _____
 _____     _ _    _____                     _|___  |
|  _  |_ _| | |  | __  |___ ___ _ _ ___ ___| |_|  _|
|   __| | | | |  |    -| -_| . | | | -_|_ -|  _|_|
|__|  |___|_|_|  |__|__|___|_  |___|___|___|_| |_|
                             |_|
```