NuGet package

This branch implements everything mentioned in issue #17, so I believe that can be closed once this is merged. When it is, I'll rejig the required stuff in [TeamCity](http://teamcity.codebetter.com/project.html?projectId=project344) to create a NuGet package from master. I will also try to delete the [raven-csharp package](https://www.nuget.org/packages/raven-csharp/) so there won't be any confusion over which package is the official one.