Branch for developing mauve further

It doesn't seem like we're near a consensus on either the approach to
solve the issue, nor what the solution's name should be if we end up
putting reftype et al. into a module (although ref:: seems to be
favoured by many right now). We really don't want to release with a
module in a temporary namespace, and rushing for a solution doesn't seem
like a great idea either. We still have plenty of release-cycles left
until 5.14 next year.

After reverting it in blead, I re-applied it, and pushed the result to a
branch called `mauve' for further development of that approach. Feel
free to rebase that onto blead, if necessary.

If we end up not using the mauve approach, also feel free to delete that
branch at some point. All its history is available in blead anyway.

• Branch for developing mauve further by Florian Ragwitz