SI-8113 scaladoc: allow a newline between a link target and title

Parsing `[[http://foo.bar link title]]` stops at the first whitespace.
This breaks pretty badly in:
```
[[http://foo.bar
link title]]
```
It stops after "link", interprets what it parsed as a link to a member,
obviously fails, and then just ouputs "title".
It should at least return a proper error, or, even better, just allow a
newline between the target and title. I went for the latter.