I scoured the net (w Google anyway) to find some association with ABC notation and guitar fretboard diagrams being able to be included in the standard.
The closest I found was hudsonlacerda's website but there was no answer as to how to best implement a tar.gz file he supplied on his website.
It seemed there has been changes to his website too that prohibited some links. (404 page)
I think lilypond has guitar diagrams but it seems as if we have to turn ourselves into a pretzel just to get going with ABC.
And lilypond is reserved for an elite class. No offense lilyponders.
Guitar diagrams are being developed by volunteers at MusicScore but it is only untill MusicScore 2.0. they will reportedly see them.
They just released v. 1.3 and there is no forthcoming info on just how realistic MusicScore 2.0 will be.
I mean if it will be released anytime soon.
As a teacher, chord diagrams would be an unbelievable tool.