Ported to NET 3.0

[wonea]

I've

• Ported this to NET Core 3.0 by re-doin the project files in the new format
• Now using VS to generate the NuGet packages
• Adjusted the NuGet package to include NET Core 3.0 as well.

Newly generated NuGet packages can be found here

Please merge this and publish a new NuGet when your ready.

[bblanchon]

Awesome! Can you delete .nuget/nuget.exe as well?

[wonea]

@bblanchon Done.