Add build script to automate compile and nupkg creation.

[pbolduc]

Added build script to automate creation of new nupkg. Follows model used by Newtonsoft.Json and others. Run build\runbuild.cmd and the project will be compiled and nuget package created in Working\NuGet\

Note: build\build.ps1 has the version of the package to be created so that the nuspec file does not need to be updated unless you want to include release notes, etc.