Check documentation for broken links

[hannobraun]

Since intra-doc links are about to be stable, I didn't make the effort to properly link various items in the documentation. This should fix itself soon, but I'm not sure with which release.

[jessebraham]

This feature seems to have landed in 1.48, which released today.

[hannobraun]

Excellent! I'll leave this issue open until someone had a chance to look over the documentation. There are probably still some broken links, where the linked type is not in scope.