*     .url("http://publicobject.com/helloworld.txt")
 *     .build();
 * ```
 *
 * The [CacheControl] class can configure request caching directives and parse response caching
 * directives. It even offers convenient constants [CacheControl.FORCE_NETWORK] and
 * [CacheControl.FORCE_CACHE] that address the use cases above.
 *
 * [rfc_7234]: http://tools.ietf.org/html/rfc7234
 */
class Cache internal constructor(