DOC: Fix LabelBinarizer docstring to rst format bug

Also add line to make multilabel classification example more instructive

Before:
![selection_002](https://cloud.githubusercontent.com/assets/1284973/5189062/c35a7a1e-74a8-11e4-93a0-c7888a895bb8.png)

After:
![selection_003](https://cloud.githubusercontent.com/assets/1284973/5189069/cbd31ec6-74a8-11e4-84e9-332af60869bd.png)