Support nuget contentFiles, used for some project types

[supergibbs]

I received the following message:

Hello,

I am PM with the NuGet team and I have seen multiple users complaining about the package not working with new project system (i.e. with Packagereference). E.g: https://twitter.com/caycedo/status/1011991725378809856

It would really help if you could update the package to contain another folder 'contentFiles' with all the contents in the 'content' folder? This will solve a lot of customers' pain. Let me know if I can help in anyway.

Thanks, Anand Gaurav PM | NuGet