Updated the buildpackage docs
Removed the -prerelease switch from this script
- it was not flexible enough, we need multiple prereleases with different names
- the -v switch achieves this by allowing you to specify any version number/name
- better docs now explain how to use -v to generate a named prerelease build
Merge pull request #150 from AnthonySteele/nuget_docs_update

Nuget docs update