Adds the CHANGELOG.md.

CHANGELOG.md

@@ -0,0 +1,25 @@
+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [keep a changelog][xtlink-keep-a-changelog]
+and this project adheres to [Semantic Versioning 2.0.0][xtlink-semantic-versioning].
+
+## [1.0.0] - 2019-08-07
+
+### Added
+
+* `JsonEncoderOptions` representing PHP's native JSON encoding options
+* `JsonDecoderOptions` representing PHP's native JSON decoding options
+* `JsonEncoder` encodes values into a JSON string
+* `JsonDecoder` decodes values from a JSON string
+* `PHPUnit` tests
+* `README.md`
+* `CHANGELOG.md`
+
+[1.0.0]: https://github.com/codekandis/json-codec/tree/1.0.0
+
+
+
+[xtlink-keep-a-changelog]: http://keepachangelog.com/en/1.0.0/
+[xtlink-semantic-versioning]: http://semver.org/spec/v2.0.0.html