nuget packages and build script

Scripts to build and publish NuGet packages for Boo.

I've setup a [test gallery](https://www.myget.org/gallery/drslump-testing) to play with them, although I think you should publish them on the official NuGet repository for easier access.

You can use the following command to update them in the test gallery:

    nant -D:nuget.feed=https://www.myget.org/F/drslump-testing -D:nuget.apikey=cf7f9f55-1784-4e77-a3fa-5a6c98ca24db publish