Fix "Keep a Changelog" format

- Add "Unreleased" link
- Remove non-existing link for first version
- Prepare linking of v1.1.0

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
-## [1.0.0] - 2018-02-21
+## 1.0.0 - 2018-02-21
 ### Added
 - Initial version uploaded to CTAN.
+
+[Unreleased]: https://github.com/adbrucker/authorarchive/compare/v1.0.0...HEAD
+[1.1.0]: https://github.com/adbrucker/authorarchive/compare/v1.0.0...v1.1.0