upgrade SDK project to .NET Standard 2.1 and Tests and Examples proje…

[pundj]

…cts to .NET 5.0

[pundj]

I did not mess with package version numbers because that should be up to you as to how you want to version these. This is a fix for #5

[mmollick]

Hey @pundj thanks for putting this together. Doing some quick reading over .Net 5, it seems .Net Framework 4 is still supported.
Would the updates you've made allow this package to continue to work in .Net Framework 4? Or would this break support for it?

[pundj]

@mmollick Well, after looking further, it seems .NET Standard 2.1 is only compatible with .NET Core 3.0 and up and not compatible at all with .NET Framework. So, as mentioned in #5, it might be good to create a new repo where you have a separate package with support for .NET Core and .NET (Microsoft unified .NET Framework and .NET Core into a single .NET, which right now the latest supported version is .NET 5, and are putting all their eggs in that basket going forward).

Alternatively, if I downgrade the SDK project to target .NET Standard 2.0 instead of 2.1, that would be compatible with .NET 5 and up, .NET Core 2.0 and up, and .NET Framework 4.6.1 and up. Support chart here: .NET Standard Implementation Support

It would be very easy to downgrade from 2.1 to 2.0 if you want. Or if you would like to create a new repo, you could use this code as a starting point, depending on what .NET Core and unified .NET versions you're hoping to target.

[KeithHenry]

I've gone a bit further and applied a proper .NET upgrade in https://github.com/EvolutionJobs/NeverBounce

I've applied that fork back here in #20