Autogenerate table using data scraped from EC2 

This PR:

-  Adds a script (`scrape.py`) which scrapes information from http://aws.amazon.com/ec2/instance-types/, http://aws.amazon.com/ec2/pricing/pricing-on-demand-instances.json, and http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/using-eni.html to automatically collect information about available instance types and pricing.
- Replaces `index.html` with a Mako template, and adds a script (`render.py`) to render the template, using the JSON output from the previous script
- Adds pricing (and availability) data for every region, and enables the "Region" dropdown.

You can see a demo of the result here: https://nelhage.com/ec2instances/
Including the generated JSON file (Deliberately hosted in the output, in case it's useful for anyone else: https://nelhage.com/ec2instances/instances.json)

The intent here is that the generation can be done offline, and will still produce a static site under `www/` that can be hosted from s3 as before.