Update Changelog for release of version 3.0.0

CHANGELOG.md

@@ -2,6 +2,17 @@
 
 All notable changes to the LaunchDarkly Go SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+[3.0.0] - 2018-02-19
+
+### Added
+- Support for a new LaunchDarkly feature: reusable user segments.
+- The mechanism by which the client retrieves feature and segment data from the server is now customizable through an interface, `UpdateProcessor`. This will be used in future to support test fixtures.
+
+### Changed
+- The `FeatureStore` interface has been changed to support user segment data as well as feature flags. Existing code that uses `InMemoryFeatureStore` or `RedisFeatureStore` should work as before, but custom feature store implementations will need to be updated.
+- Logging is now done through an interface, `Logger`, instead of directly referencing `log.Logger`. Existing code that uses `log.Logger` should still work as before.
+
+
 
 ## [2.3.0] - 2018-01-31