* Added a trailing `\r\n` to multipart/form-data payloads. See
https://github.com/guzzle/guzzle/pull/871
* Added a `GuzzleHttp\Pool::send()` convenience method to match the docs.
* Status codes are now returned as integers. See
https://github.com/guzzle/guzzle/issues/881
* No longer overwriting an existing `application/x-www-form-urlencoded` header
when sending POST requests, allowing for customized headers. See
https://github.com/guzzle/guzzle/issues/877
* Improved query string and path URL serialization.
* No longer double percent-encoding characters in the path or query string if
they are already encoded.
* Now properly encoding the supplied path to a URL object, instead of only
encoding ' ' and '?'.
* Now allowing many more characters to be present in the query string without
being percent encoded. See http://tools.ietf.org/html/rfc3986#appendix-A