* Pool class no longer uses recursion when a request is intercepted.
* The size of a Pool can now be dynamically adjusted using a callback.
  See https://github.com/guzzle/guzzle/pull/943.
* Setting a request option to `null` when creating a request with a client will
  ensure that the option is not set. This allows you to overwrite default
  request options on a per-request basis.
  See https://github.com/guzzle/guzzle/pull/937.
* Added the ability to limit which protocols are allowed for redirects by
  specifying a `protocols` array in the `allow_redirects` request option.
* Nested futures due to retries are now resolved when waiting for synchronous
  responses. See https://github.com/guzzle/guzzle/pull/947.
* `"0"` is now an allowed URI path. See
  https://github.com/guzzle/guzzle/pull/935.
* `Query` no longer typehints on the `$query` argument in the constructor,
  allowing for strings and arrays.
* Exceptions thrown in the `end` event are now correctly wrapped with Guzzle
  specific exceptions if necessary.
