* Feature: Added the `on_stats` request option to provide access to t…

…ransfer

  statistics for requests. guzzle#1202
* Feature: Added the ability to persist session cookies in CookieJars.
  guzzle#1195
* Feature: Some compatibility updates for Google APP Engine
  guzzle#1216
* Feature: Added support for NO_PROXY to prevent the use of a proxy based on
  a simple set of rules. guzzle#1197
* Feature: Cookies can now contain square brackets.
  guzzle#1237
* Bug fix: Now correctly parsing `=` inside of quotes in Cookies.
  guzzle#1232
* Bug fix: Cusotm cURL options now correctly override curl options of the
  same name. guzzle#1221
* Bug fix: Content-Type header is now added when using an explicitly provided
  multipart body. guzzle#1218
* Bug fix: Now ignoring Set-Cookie headers that have no name.
* Bug fix: Reason phrase is no longer cast to an int in some cases in the
  cURL handler. guzzle#1187
* Bug fix: Remove the Authorization header when redirecting if the Host
  header changes. guzzle#1207
* Bug fix: Cookie path matching fixes
  guzzle#1129
* Bug fix: Fixing the cURL `body_as_string` setting
  guzzle#1201
* Bug fix: quotes are no longer stripped when parsing cookies.
  guzzle#1172
* Bug fix: `form_params` and `query` now always uses the `&` separator.
  guzzle#1163
* Bug fix: Adding a Content-Length to PHP stream wrapper requests if not set.
  guzzle#1189

* Fixed a memory leak in the curl handlers in which references to cal…

…lbacks

  were not being removed by `curl_reset`.
* Cookies are now extracted properly before redirects.
* Cookies now allow more character ranges.
* Decoded Content-Encoding responses are now modified to correctly reflect
  their state if the encoding was automatically removed by a handler. This
  means that the `Content-Encoding` header may be removed an the
  `Content-Length` modified to reflect the message size after removing the
  encoding.
* Added a more explicit error message when trying to use `form_params` and
  `multipart` in the same request.
* Several fixes for HHVM support.
* Functions are now conditionally required using an additional level of
  indirection to help with global Composer installations.

* Fixed a bug with serializing the `query` request option where the `&`

  separator was missing.
* Added a better error message for when `body` is provided as an array. Please
  use `form_params` or `multipart` instead.
* Various doc fixes.

Adding version guidance to readme

* Mock now supports `save_to`

* Marked `AbstractRequestEvent::getTransaction()` as public.
* Fixed a bug in which multiple headers using different casing would overwrite
  previous headers in the associative array.
* Added `Utils::getDefaultHandler()`
* Marked `GuzzleHttp\Client::getDefaultUserAgent` as deprecated.
* URL scheme is now always lowercased.

* Added `AppliesHeadersInterface` to make applying headers to a reque…

…st based

  on the body more generic and not specific to `PostBodyInterface`.
* Reduced the number of stack frames needed to send requests.
* Nested futures are now resolved in the client rather than the RequestFsm
* Finishing state transitions is now handled in the RequestFsm rather than the
  RingBridge.
* Added a guard in the Pool class to not use recursion for request retries.

* 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 guzzle#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 guzzle#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 guzzle#947.
* `"0"` is now an allowed URI path. See
  guzzle#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.

This change updates query strings so that they are treated as un-enco…

…ded values

by default where the value represents an un-encoded value to send over the
wire. A Query object then encodes the value before sending over the wire. This
means that even value query string values (e.g., ":") are url encoded. This
makes the Query class match PHP's http_build_query function. However, if you
want to send requests over the wire using valid query string characters that do
not need to be encoded, then you can provide a string to Url::setQuery() and
pass true as the second argument to specify that the query string is a raw
string that should not be parsed or encoded (unless a call to getQuery() is
subsequently made, forcing the query-string to be converted into a Query
object).

* Added a trailing `\r\n` to multipart/form-data payloads. See

  guzzle#871
* Added a `GuzzleHttp\Pool::send()` convenience method to match the docs.
* Status codes are now returned as integers. See
  guzzle#881
* No longer overwriting an existing `application/x-www-form-urlencoded` header
  when sending POST requests, allowing for customized headers. See
  guzzle#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

Prepping bugfix release