Added embed example.

This is WIP, but the main idea is to show how to use the new embed API to do nice things...
Here, I wrote a simple Flask app that renders a Reveal.js slidedeck showcasing Bokeh plots :wink:
There are a lot of things to make better, but I want an early feedback, jeje...
Just look at it and let me know what do you think... and how to improve it.