docs: reformat CHANGELOG

CHANGELOG.md

-# Change Log
-All notable changes to this project will be documented in this file.
+## [v2.1.0](https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v2.1.0)
 
-## [Unreleased]
-#### Added
-- Added another template with option of a configurable message
+### Added
 
-## [v2.1.0]
-#### Added
 - Added .gitignore
 
-#### Changed
+### Changed
+
 - Double quotes changed to single quotes
 - Using of short array syntax (from array() to [])
 - Code improvements
 
-## [v2.0.0]
-#### Added
+## [v2.0.0](https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v2.0.0)
+
+### Added
+
 - Added file phpcs.xml
 
-#### Changed
+### Changed
+
 - Changed code style to PSR-2
 - Module uses namespaces
 
-## [v1.1.1]
-#### Changed
+## [v1.1.1](https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v1.1.1)
+
+### Changed
+
 - Changed header in perunauthorize_403.php
 
-## [v1.1.0]
-#### Added
+## [v1.1.0](https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v1.1.0)
+
+### Added
+
 - Czech translation
 
-#### Changed
+### Changed
+
 - Classes SimpleSAML_Logger and SimpleSAML_Module renamed to SimpleSAML\Logger and SimpleSAML\Module
 - Removed Perunauthorize.translation.json
 
-## [v1.0.0]
-#### Added
-- Changelog
+## [v1.0.0](https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v1.0.0)
+
+### Added
 
-[Unreleased]: https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/master
-[v2.1.0]: https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v2.1.0
-[v2.0.0]: https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v2.0.0
-[v1.1.1]: https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v1.1.1
-[v1.1.0]: https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v1.1.0
-[v1.0.0]: https://github.com/CESNET/perunauthorize-simplesamlphp-module/tree/v1.0.0
+- Changelog