Fix build for FSharp3 branch

This commit only requires NuGet.exe committed in the repo. It pulls FAKE in the build.bat script. Also, the build creates a NuGet package, which I have not yet published. If you would like to do so, you can pass your NuGet key like so: `.\build.bat nugetkey {your-nuget-key}`. (You may need to precede `nugetkey` with a `/` or `-`.)