#764 Link checking in Examples

[Hugh A. Cayless]

Followup from [bugs:#744].

See Martin's comment from that bug:

Just did it as a test:
119 links checked. 22 warnings found. 43 errors found.
There are over 400 links, but most are duplicates; many are not intended to work (www.example.com etc.).
Should be possible to add this into the system, filtering out the example.com ones. I'm going to re-open this bug and assign it to myself to do that.