Add release notes and update format

Author: piotrmurach

CHANGELOG.md

@@ -1,5 +1,21 @@
-0.2.0 (January 3, 2015)
+# Change log
+
+## [v0.3.0] - 2019-02-26
+
+* Change to limit to Ruby >= 2.0.0
+* Change gemspec to load files directly without git
+* Change to freeze all strings
+
+## [v0.2.0] - 2015-01-03
 
 * Add ability to set default through value and block
 * Add ability to iterate over keys and values
 * Add to_hash export
+
+## [v0.1.0] - 2014-12-27
+
+* Initial implementation and release
+
+[v0.3.0]: https://github.com/piotrmurach/splay_tree/compare/v0.2.0...v0.3.0
+[v0.2.0]: https://github.com/piotrmurach/splay_tree/compare/v0.1.0...v0.2.0
+[v0.1.0]: https://github.com/piotrmurach/splay_tree/compare/v0.1.0