Add Cyberwizzards lookahead. Thanks a lot, Cyberwizzard.

For now only the two new files, tweaked a bit in the #ifdef
area to let them compile without LOOKAHEAD being defined.
Make lookahead basically working.

This means, modify existing code to let the lookahead algorithms
do their work. It also means to remove some unused code in
dda_lookahead.c and reordering some code to make it work with
LOOKAHEAD undefined.
Bring LOOKAHEAD into the config templates.