Migration to .NET Standard 2.0

[ktos]

The package now supports .NET Standard 2.0, so it is available for Xamarin, Unity, UWP, etc. (and is not showing errors in .NET 5 or later anymore).

[ktos]

Zamiast Nuget.Build.Packaging teraz buduje się paczkę używając standardowego polecenia w .NET 5 - po prostu dotnet pack i dostajesz .nupkg.

[Mondonno]

@ktos i saw that you migrated the files from Airly.Net/contents/* to Airly.Net/* why? Also what's changing with deleting the assembly info file and why you deleted it? All other things looks very good 👍

[Mondonno]

Please explain deletion of AssemblyInfo.cs, packages.config, also visual studio have some realy strange things when the test imported project does not depend on the same packages as the main project. Also explain the migration as i mentioned above. As I said above all other things look good 💯

[ktos]

• packages.config is not needed anymore, in new project system dependencies are in the .csproj file,
• AssemblyInfo.cs was empty (identical to the default one), now it should be generated automatically during compilation,
• Moving from content/ - I thought you moved everything to content/ to avoid source code merging with project configuration (e.g. packages.config). I think we can move it back, it does not matter actually,
• dotnet test had no problems after removing dependency - I've not tested on VS for Mac; it can be reverted, but the dependent version must be the same (13.0.0.2) as the original version (and was something like 12.0.0.0 and it conflicted).

[Mondonno]

All unit-tests passed on my side 👍
So i think i'm able to merge this PR #1