I am learning ASP.NET Core 1.0 (vNext). With that in mind, I have a solution that is structured like this:
MySolution
src
MyLibrary
MyClass.cs
You don't have to publish the package to NuGet if you don't want to share it with other people/projects outside of your solution. You can just reference the package directly from source.
However, if that still doesn't work for you then you have three options: