C# 5 migration aids

[sharwell]

A lesser-considered option is the inverse of #19. It would be cool to be able to install a NuGet package with analyzers and code fixes that identify the use of C# 6 features and (where possible) propose code fixes to convert those features to the equivalent syntax in C# 5. This allows developers to work efficiently within Visual Studio 2015, and then "press a button" to transform their work output into a form that compiles with older versions of Visual Studio.