Implemented dictionary lookup and example use.

To get you going I've implemented the dictionary look up.  I waited to do this because I wanted you to read more of the documentation first, and since you've done that you're now in a better position to understand the code.  A good skill to have is reading other people's code: I don't expect you to understand everything I've written, so please ask questions where things are unclear.  But run the code and play around with the `data` variable first to discover answers to your questions.