Add a minimal Visual Studio project file

For developers working with Visual Studio there has to be a file that
allows them to use the IDE without leaving NAnt out. So create a project
file for Visual Studio and add common tasks that can be called by Visual
Studio and call the respective nant targets.
Make the build file smarter

The build file should provide a help target that helps users with
building the project. The build target should also create an
AssemblyInfo file to be included in build process.