Issue title: Ensure rainbow works in VS2015.1 C# Interactive
 Issue body: VS2015.1 brings roslyn into the C# Interactive window, so it now has code colorization: http://blogs.msdn.com/b/dotnet/archive/2015/11/24/what-s-new-in-visual-studio-update-1-for-net-managed-languages.aspx

Need to test and ensure Viasfora works in there too.
 Comments: 
 Comment 0: Tested and works fine:
![image](https://cloud.githubusercontent.com/assets/16179/11550097/37b344e8-993a-11e5-8d7a-010f74297c92.png)

{'source': 'GithubIssues', 'repo_name_with_owner': 'tomasr/viasfora', 'issue_id': 119561021, 'repo_stars': 477.0}