R1:349f006904fa

Remarkup: make less internal links open in new tabs

Summary:
This is an attempt to improve the default behavior in Remarkup about
links. It does not change any behaviors manually specified in the engine
and it does not change any behaviors related to external domains.

As default, now these kind of links will open in the same tab:

- anchors
- relative URLs
- absolute URLs pointing to the base-URI domain

All the other cases are kept as before - so they open in another tab.

In short, assuming you are we.