changelog: add diff links

CHANGELOG.md

@@ -5,17 +5,24 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
-## [1.2.0] 2019-11-05
+## [Unreleased]
+
+## [1.2.0] - 2019-11-05
 ### Added
 - Support for Mac OS X
 
-## [1.1.0] 2019-09-03
+## [1.1.0] - 2019-09-03
 ### Added
 - Prepare push to pypi.org
   - Converted readme from markdown to ReSructuredText format
   - Added module metadata (author, maintainer, url)
 
-## [1.0.0] 2019-09-03
+## [1.0.0] - 2019-09-03
 ### Added
 - Class `DLInfo`
   - Property `path` returns absolute path to dynamically loaded library
+
+[Unreleased]: https://github.com/cloudflightio/python-dlinfo/compare/v1.2.0...HEAD
+[0.1.2]: https://github.com/cloudflightio/python-dlinfo/compare/v1.1.0...v1.2.0
+[0.1.1]: https://github.com/cloudflightio/python-dlinfo/compare/v1.0.0...v1.1.0
+[0.1.0]: https://github.com/cloudflightio/python-dlinfo/releases/tag/v1.0.0