Restore 0.9.0 changelog notes

CHANGELOG.md

@@ -51,3 +51,21 @@
 * Switch README from .rst to .md format 
 * Update dependencies
 * Add command to handler call to provide support for GuzzleServices
+
+## 0.9.0 - 2016-01-30
+
+* Updated to use Guzzle 6 and PSR-7.
+* Event system has been replaced with a middleware system
+    * Middleware at the command layer work the same as middleware from the
+      HTTP layer, but work with `Command` and `Result` objects instead of
+      `Request` and `Response` objects
+    * The command middleware is in a separate `HandlerStack` instance than the
+      HTTP middleware.
+* `Result` objects are the result of executing a `Command` and are used to hold
+  the parsed response data.
+* Asynchronous code now uses the `guzzlehttp/promises` package instead of
+  `guzzlehttp/ringphp`, which means that asynchronous results are implemented
+  as Promises/A+ compliant `Promise` objects, instead of futures.
+* The existing `Subscriber`s were removed.
+* The `ServiceClientInterface` and `ServiceClient` class now provide the basic
+  foundation of a web service client.