prepare first stable release (#8)

Author: dbu

CHANGELOG.md

@@ -5,6 +5,10 @@ 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).
 
+## [1.0.0] - 2021-03-09
+
+- Stable release - no changes since 0.1.1
+
 ## [0.1.1] - 2020-10-21
 
 * Allow installation with PHP 8