Adding quick way to navigate between commonly used directories

Original article: http://jeroenjanssens.com/2013/08/16/quickly-navigate-your-filesystem-from-the-command-line.html
Discusion on hacker news: https://news.ycombinator.com/item?id=6229001
Discussion on reddit: http://www.reddit.com/r/programming/comments/1kmjb7/quickly_navigate_your_filesystem_from_the/