Change jellyfish to fetch data asynchronously

This changes jellyfish to fetch data asynchronously, not as part of the request flow.

Also cleaned up a good bit of cruft around the code, hopefully making it easier to read and understand what is happening.
LICENSE ftw!
Code review comments
Add installation and running instructions to the README
Merge pull request #11 from tidepool-org/cheddar/async-fetch

Change jellyfish to fetch data asynchronously