DOC add copybutton to code examples

This adds a non-intrusive button to codeblocks in the docs

It hides the `.>>>' ect and makes it easy to copy into ipython

See [scipy-lecture-notes](http://scipy-lectures.github.io/intro/language/control_flow.html#while-break-continue) for an example of this.

![screenshot at 2013-10-14 09 32 35](https://f.cloud.github.com/assets/1378870/1323993/120cc974-34a3-11e3-8afc-040122d35b85.png)

becomes

![screenshot at 2013-10-14 09 32 46](https://f.cloud.github.com/assets/1378870/1323996/1aad8334-34a3-11e3-9dfe-0dd21dc9c42e.png)