Crit-bit tree

http://cr.yp.to/critbit.html
https://github.com/agl/critbit

Original code is taken from Dan Bernstein's qhasm. Adam Langley's CWEB sources
were converted to human parsable C adding easy to use interface for string,
buffer and integer keys.

This code, like Prof. Bernstein's original code, is released into the public
domain.