Merge pull request win-acme#1252 from PKISharp/core-3

Promote .NET Core 3 version (2.1.x) to master in preparation of release

Renewals happened whenever they were *not* due

second try to fix conditional compilation

second try to fix conditional compilation

Implement POST-as-GET setting

dual-target plugins

another try at git submodules

Merge pull request win-acme#1182 from PKISharp/master

dns patch

Update appveyor.yml

Rename function to be consistant with others