add changelog for v1.0 release (#174)

Author: meiliang86

CHANGELOG.md

@@ -0,0 +1,13 @@
+# Changelog
+
+## v1.0.0 (06-04-2018)
+
+### Features
+- POJO workflow, child workflow, activity execution.
+- Sync and Async workflow execution.
+- Query and Signal workflow execution.
+- Test framework.
+- Metrics and Logging support in client.
+- Side effects, mutable side effects, random uuid and workflow getVersion support.
+- Activity heartbeat throttling.
+- Deterministic retry of failed operation.