Introduce CHANGELOG.md so next time I have to make a release I don't look like an idiot

CHANGELOG.md

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+# Changelog
+
+This file always reflects the *latest* changes up until a release. Then it gets wiped out and updated again.
+
+## Changes
+
+* Update SDL to version 3
+* Screen no longer black when the game is paused
+* Other minor fixes such as:
+    - Fix crashes when closing the emulator while a game is running
+    - Remove `nativefiledialog-extended` submodule as it is no longer needed
+    - Update `xbyak` subtree
+    - Small CMake refactoring