Update to DDOX 0.9.19 with multiple declarations per page support.

 - Fixes the code that implants a link into the page title
 - Includes dub.selections.json, to make sure everyone uses the same dependencies.
Merge pull request #129 from s-ludwig/master

Update to DDOX 0.9.19 with multiple declarations per page support.
Update to ddox 0.9.20.

There was a missing file in DDOX 0.9.19.
Merge pull request #130 from s-ludwig/master

[trivial] Update to ddox 0.9.20.