Provide samples for coding against NuGet 3 codebase

Need to enumerate common scenarios we want to show as samples, going to take a quick stab and will keep refining as feedback comes in

• Get latest version for a given package ID
• Search results for a given search string
• Download a package given ID and version (or just ID and get latest)
• Restore a project.json
• Restore a packages.config
• Control package extraction mode

Would be nice to contrast samples from nuget.core with the NuGet3 codebase.

We will gladly take pull requests to https://github.com/NuGet/docs.microsoft.com-nuget as folks find good ways to port over, and of course sample projects to https://github.com/nuget/samples utilizing the new API. I'm also open to running a CI on top of the samples to ensure breaking changes are at least known, if not immediately addressed.