Ref12 3.0

• F12 jumps to Roslyn source code! 👏
  Many thanks to @DustinCampbell, @jasonmalinowski, @KirillOsenkov, @Pilchie, and the rest of the Roslyn team!
• Ref12 now works with the Roslyn End-User Preview installed
• Duplicate log output is no longer emitted when nothing changes (#3)