Fix "Keep a Changelog" format

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

This commit manually applies pull request https://github.com/adbrucker/llncsconf/pull/9/.

CHANGELOG.md

@@ -4,10 +4,11 @@ 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).
 
-## [1.0.1] - 2018-02-21
-### Changed
-- Fixed version information in ProvideClass{}[].
+## [Unreleased]
 
-## [1.0.0] - 2018-02-20
+## 1.0.0 - 2018-02-20
 ### Added
 - Initial version uploaded to CTAN.
+
+[Unreleased]: https://github.com/adbrucker/llncsconf/compare/v1.0.0...HEAD
+[1.1.0]: https://github.com/adbrucker/llncsconf/compare/v1.0.0...v1.1.0