Nuget packager

NuGet packager project (currently attached to the MonoGame.Framework.sln) for Windows platforms

Currently supports:
* WindowsGL
* Windows 8
* Windows Phone

Also included a built package for the current 3.0.1 release

The packager builds a pre-release package (set in the version of the NuSpec) to allow for current Dev builds.  Production builds would just update the version for a release.

*Note to run in Visual Studio you will need the "Nuget Packager" Extension installed in VS

Will next work on Binaries only packages