Prepare for release

Author: BenMorel

CHANGELOG.md

@@ -2,11 +2,11 @@
 
 All notable changes to this project will be documented in this file.
 
-## Unreleased
+## [0.9.3](https://github.com/brick/math/releases/tag/0.9.3) - 2021-08-15
 
 🚀 **Compatibility with PHP 8.1**
 
-- Removes a warning on PHP 8.1 due to the `Serializable` interface being deprecated (thanks @TRowbotham)
+- Support for custom object serialization; this removes a warning on PHP 8.1 due to the `Serializable` interface being deprecated (thanks @TRowbotham)
 
 ## [0.9.2](https://github.com/brick/math/releases/tag/0.9.2) - 2021-01-20