chore:setup.py: bump version number

Update (or, more correctly, create) the changelog in the process.

CHANGELOG.md

+# Changelog
+
+## 0.0.3
+
+Added:
+
+- A changelog.

setup.py

@@ -20,7 +20,7 @@ setup(
     long_description=open('README.md').read(),
     long_description_content_type='text/markdown',
     url='https://gitlab.developers.cam.ac.uk/uis/devops/django/api-gateway-auth',
-    version='0.0.2',
+    version='0.0.3',
     license='MIT',
     author='DevOps Division, University Information Services, University of Cambridge',
     author_email='devops@uis.cam.ac.uk',