Makes the project compatible with 2012

I just changed all the refs to version "12.0" to "11.0".  Seems like it works fine in 2012 now, but I don't have 2013 to test with to make sure it still works there.

If this isn't a good way to do this, is there a better way to manage extensions across different versions of VS?  A separate project for each version with the files linked in?  Just thinking out loud.

Thanks,
John Bubriski