Post about Theano metaoptimization

This is my guest post about Theano's new meta-optimization feature. It's not finished yet, but maybe you want to have a look at it already. I'll see if I can finish it today, but probably it will be tomorrow (I'll rename the file accordingly then).
When trying it, better download the file to your local checkout rather than checking out my branch; I might force-push to this branch when I'm done.

TODO:
* [x] Implementation section
* [x] Practical gains section
* [x] Future section
* [x] Think about removing the need for / shortening the "for the eager ones" paragraphs