Extract NuGetPackageBuilder from NuGetCommands
Cover NuGet package builder with test
Add NuGet.Core package
Switch to using NuGet.Core for NuGet pack instead of command line NuGet.exe
Split NuGetPackCmdConfigurator into the configurator and the immutable specification
Include NuGet.Core as package dependency, and remove unused NuGet.exe binary
Completed acceptance test for NuGet packaging task