*  New: Prevent OkHttp from retransmitting a request body by overriding `RequestBody.isOneShot()`.
    This is most useful when writing the request body is destructive.

 *  New: We've added `requestFailed()` and `responseFailed()` methods to `EventListener`. These
    are called instead of `requestBodyEnd()` and `responseBodyEnd()` in some failure situations.