Instructions for upgrading to version 3 and 4

[wesleykendall]

Instructions for upgrading to version 3 and 4

[davecoates]

These changes are great @wesleykendall - thanks very much

One thing we encountered was that a couple of trigger had a name change so after migrating the old triggers still existed. Specially these were for some m2m through models I created new proxy models for as part of these changes. We had to manually run a prune to clean them up. Might be worth mentioning this in the upgrade notes?

[wesleykendall]

@davecoates thanks so much for bringing this to my attention. I will update the upgrade notes here and in the official docs today. It totally slipped my mind that the trigger names would change, causing a need to prune old ones that weren't tracked in migrations. My apologies if this caused you trouble or errors in your application.

BTW I'm integrating django-pgtrigger with Django's check framework. I'm planning to add a special check to the manage.py check --deploy command while also exposing a pgtrigger check command. It will fail if there are any triggers that are outdated, uninstalled, or need to be pruned. While I don't plan to do a breaking change like this release again in the future, I hope this check will be helpful to avoid situations like what you encountered. Feedback is welcome!

[wesleykendall]

Added a third bullet point to the migration notes and also updated it in the FAQ in #94