.NET Standard support?

[YoshiRulz]

Is it possible to add a netstandard2.0 or net461 target? I can immediately see NativeLibrary as being a problem, but I think you can achieve the same thing with the older APIs, they just might not be in .NET Standard. Some of the Span extensions might not be available in the polyfill either.

Unrelated, it would be helpful to link to the repo from the NuGet page and vice-versa.