ENH: source decoding example

Here's our first source decoding example, I hope you're going to like it.

![source_decoding_l](https://f.cloud.github.com/assets/1908618/412051/7e16925a-ab9e-11e2-9550-6267a3f890c9.png)
![source_decoding_o](https://f.cloud.github.com/assets/1908618/412052/7eb00dcc-ab9e-11e2-824d-3ed32b0cf734.png)