Updated fetcher to handle fetched documents that produced an error.
Created Cache Utility == #13

The cache utility acts as a middleman between applications that
use the API cache and the API itself. Things it does:

* Handles cache key prefixes
* Allows outside applications to change key prefixes. For example,
  the API cache cleaner can up the store prefix when it is creating
  a new cache and then up the fetch prefix when it has completed.
  This causes 0 downtime for the cache.
* Handles processing of request parameters
* Handles fetching, storing, deleting of items in the cache.
Hooked up parts of the API to new Cache utility -- #13