when looping through the tree, the algorithm would stop, if found a '\0'
in the key of the tree node. there should be no "child" field after a '\0',
but "next" fields may exist.

so, this is basically what happens when you don't have anything better
to do in the christmas weekend. most of this code was written in the
last 2 or 3 days.

i'd like to thank the chivas brothers, the weather and my psychological
problems for this achievement.

on a serious note, this tool still needs a man page, more tests, and the
aws lambda function should be adapted to use it instead of (or together
with) make/busybox.

also, while talking about aws lambda, this tool can be nicely embedded
into the blogc binary, to produce a single "small" static binary for
usage in lambda ;)