Building and publishing a nuget package

[atrauzzi]

Would absolutely love to know more about how one would go about taking a project.json project and building and publishing it as a nuget package. Lots of little in-between things to cover I'm sure.

This might do well as a whole section, broken down into various activities:

• Building the package and dealing with target platforms
• Publishing publicly
• Publishing to a private repository
• Setting up or what to look for in a build server
• If applicable, any caveats to consuming the project from a .csproj (use a Xamarin project as an example)