Add extension library for Roslyn workspaces

[daveaglick]

Add an extension library that can create an AdhocWorkspace (or add a Roslyn Project to an existing workspace) given a Buildalyzer ProjectAnalyzer

[daveaglick]

@josephwoodward May want to take a look at this, I know you were talking about creating Workspaces from the build output earlier. Going to release it to NuGet, but my guess is that it'll probably need a couple more iterations to cover every case.

[josephwoodward]

Nice, I'll give it a look later.