Also support Visual Studio 2013.

This commit adds support for Visual Studio 2013 to SaveAllTheTime. According to [this post][1], the version number format has changed for VS 2013, so that a single version number now means "support this specific version only", much like [##.#] did before. The same behaviour as before can be achieved by specifying a supported version of [##.#,].

I have chosen to explicitly specify VS2012 and VS2013 only, as I have no idea whether or not SaveAllTheTime will continue to work with the next version of Visual Studio after VS2013 :smile:

## Still TODO:

 - [x] Finish installing VS 2012
 - [x] Install VS 2012 SDK
 - [x] Build in VS 2012
 - [x] Test in VS 2012
 - [x] Test in VS 2013

  [1]: http://blogs.msdn.com/b/visualstudio/archive/2013/08/08/update-for-extension-authors-vsix-manifest-version-ranges.aspx,