With most recent Roslyn preview

Not sure you want to pull into master branch though. There is one skipped test, one failed test. The fail is simple, we didn't add enough reference dlls to the compilation, but I'm not sure how it worked in the old version of Roslyn. Can review later.
Could this introduce a `NullReferenceException` opportunity if `ns.GetTypeMembers()` returns an `IEnumerable<A non covariant type>`, or is it safe to make this cast without checking?