On-demand caching vs. cache job

[caseyohara]

The Sinatra app has a tiny cache for the feed data to make requests more speedy for the user. It's set for a 3 hour expiration to keep it fresh, but unfortunately the first user to hit it has to wait while the cache rebuilds. After that it's fast as shit.

What's involved in setting up a background job to automatically rebuild the cache so we don't have to rely on a web request to kick one off?

[brycehammond]

I think we can set up a rake task and then just have a cron job set up on Heroku that runs it. Shouldn't be too difficult. I can set it up if you transfer ownership of powder over to the imulus user. I'll write another branch for pull request when it's done.