Migration guide for v5

[evenfrost]

Please implement a migration guide from v4 to v5 as have been promised in beta releases descriptions.

There is a lot of breaking changes, some of them are still undocumented (though I believe this is a different issue to be addressed), and we need to know how to harmlessly migrate to the new version.

[btyler]

Seconded. Isn't v5 supposed to drop in for v4? My code that worked with v4 is fubared.

[bmueller-sykes]

It's not a drop-in replacement, no. There were some non-trivial changes under the hood.

[TheSinding]

I second this
There was a promise that there was gonna be a migration guide for this