## Backlog

  - Move breakers.rb configuration file into rack-contrib as a middleware
    component.
  - Sample apps: Rack, Rails, Sinatra, Merb, etc.
  - Use Bacon instead of test/spec
  - Work with both memcache and memcached gems (memcached hasn't built on MacOS
    for some time now).
  - Fast path pass processing. We do a lot more than necessary just to determine
    that the response should be passed through untouched.
  - Don't purge/remove cache entries when invalidating. The entries should be
    marked as stale and be forced revalidated on the next request instead of
    being removed entirely.
  - Add missing Expires header if we have a max-age.
  - Purge/invalidate everything
  - Invalidate at the URI of the Location or Content-Location response header
    on POST, PUT, or DELETE that results in a redirect.
  - Maximum size of cached entity
  - Last-Modified factor: requests that have a Last-Modified header but no Expires
    header have a TTL assigned based on the last modified age of the response:
    TTL = (Age * Factor), or, 1h  = (10h * 0.1)
  - Run under multiple-threads with an option to lock before making requests
    to the backend. The idea is to be able to serve requests from cache in
    separate threads. This should probably be implemented as a separate
    middleware component.
  - Consider implementing ESI (http://www.w3.org/TR/esi-lang). This should
    probably be implemented as a separate middleware component.
  - Sqlite3 (meta store)
  - stale-while-revalidate
  - Serve cached copies when down (see: stale-if-error) - e.g., database
    connection drops and the cache takes over what it can.