Add EU-West region pricing

Thanks for the super-handy site!

I've added a selector option for EU West. It adds another factor to price calculation, and for *most* instances the prices match those on the AWS instance type page. There are some small discrepancies with the Windows pricing, and I think not every box is available in both regions, but generally its in pretty good shape.

While I was mucking around, I found this: https://spot-price.s3.amazonaws.com/spot.js?callback=callback&_=1369175411078

Which seems to be an API to get all the actual, canonical prices from Amazon. Could be useful for getting bona-fide pricing and instance availability for all regions.