Update CHANGELOG.md

Author: AB-xdev

CHANGELOG.md

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+## 1.0.0
+Initial release
+
+Support for Chart.js v4
+
+Noteworthy changes compared to [Chart.java](https://github.com/mdewilde/chart):
+* Changed the package to ``software.xdev.chartjs.model``
+* All charts (e.g. ``BarChart``, ``LineChart``, ...) are now inside the ``charts`` package
+* Breaking API changes due to compatibility with Chart.js v4; You may checkout the migration guides
+  * [3.x Migration Guide](https://www.chartjs.org/docs/4.3.0/migration/v3-migration.html)
+  * [4.x Migration Guide](https://www.chartjs.org/docs/4.3.0/migration/v4-migration.html)
+* JSON is no longer pretty printed by default due to performance reasons
+* Implemented integration tests