Added support for Go's repository retrieval.

 - Simply adds the relevant meta link in the project's show action.
 - Information about this meta tag can be found here:
   http://golang.org/cmd/go/#hdr-Remote_import_paths

Note I am not sure how to do unit tests for this, but I am willing to do those if someone can point me to how to do it. Also I did not update the CHANGELOG as I am not sure where to put the change. Is it under v6.5.0?