Integrate AutoNSubstitute into distribution

Hello. I've created AutoNSubstitute project - adapter for NSubstitute mocking framework to be used with AutoFixture.

While everything is working OK there are some issues: 
* I'm working on project on .NET 4.0 therefore it uses net40 version of NSubstitute, so I was forced to build AutoNSubstitute for net40 also.
* I can not just put compiled AutoNSubstitute assembly into my project's 'lib' becausse AutoFixture NuGet libs are signed. So I decided it will be better to integrate the adapter into AutoFixture codebase by yourself, so you'll sign it and publish on NuGet. So everyone will be able to use it.

Thank you for attention.