Django 4 support

What's Changed

• Provide heartbeat support for healthchecking periodic services by @vdboor in #12
• Update README for heartbeats by @vdboor in #13
• Add github actions by @mvantellingen in #16
• Django 3.1 support, dropped support for django 1.1 by @f213 in #18

New Contributors

• @f213 made their first contribution in #18

Full Changelog: 1.4.2...1.5.0