Provide line information on warnings and errors

[lawmurray]

Now that line information is preserved after parsing files, it should be possible to add line information (source file, line number) to warnings such as this:

warning: ignoring @ingroup something, no such group

[alberto-scolari]

I would take this on me, if no one else is on it.

[lawmurray]

That would be great @alberto-scolari, thanks. Assigned to you.