add changelog

Author: David Moreau

CHANGELOG.md

@@ -0,0 +1,13 @@
+CHANGELOG for 1.x.x
+===================
+
+This changelog references the relevant changes (bug and security fixes) done
+in 1.x.x minor.
+
+To get the diff for a specific change, go to https://github.com/liuggio/statsd-php-client/commit/XXX where XXX is the change hash
+To get the diff between two versions, go to https://github.com/liuggio/statsd-php-client/compare/v1.0.12...v1.0.13
+
+### 1.0.13
+  * add changelog
+  * feature StatsdService abstracting Client/Factory usage
+  * feature Deal with sampling in StatsdService