Version 4.2

Guzzle version 4.2:

* Now merging in default options using a case-insensitive comparison.
  Closes https://github.com/guzzle/guzzle/issues/767
* Added the ability to automatically decode `Content-Encoding` response bodies
  using the `decode_content` request option. This is set to `true` by default
  to decode the response body if it comes over the wire with a
  `Content-Encoding`. Set this value to `false` to disable decoding the
  response content, and pass a string to provide a request `Accept-Encoding`
  header and turn on automatic response decoding. This feature now allows you
  to pass an `Accept-Encoding` header in the headers of a request but still
  disable automatic response decoding.
  Closes https://github.com/guzzle/guzzle/issues/764
* Added the ability to throw an exception immediately when transferring
  requests in parallel. Closes https://github.com/guzzle/guzzle/issues/760
* Updating guzzlehttp/streams dependency to ~2.1
* No longer utilizing the now deprecated namespaced methods from the stream
  package.