This code is taken from Dan Bernstein's qhasm and implements a binary
crit-bit (alsa known as PATRICA) tree for |NUL| terminated strings. Crit-bit
trees are underused and it's this author's hope that a good example will aid
their adoption.

Herein is the CWEB source (critbit.w) and the derived files (critbit.pdf and
critbit.c) for those who don't wish to install CWEB and/or TeX.

If in doubt, read the PDF file.