[AD] UTF-8 routines done

[Peter Wang <novalazy@xxxxxxxxxx>]

I've finished adding all the functions that I wanted to the new UTF-8
API.  Now we just have to start using it (a review is welcome too, of
course).  If you find yourself writing some string function that could
be generally useful then we can add it.  I will work on converting
config.c tomorrow.

Peter