Port nuget to .NET core

[dzmitry-lahoda]

.NET Core csproj can have nuget build in. Really simplifies solution and does all from dotnet cli easy.

[alexeyzimarev]

Many libs that support .NET Framework use Cake or Fake to build, pack and publish. I don't think there's an issue with using Cake.

[nlkl]

I am considering refreshing the build setup a bit when I get to it, but due to all the other pending issues this is not the highest priority at the moment.

Thanks!

/ Nils