Tools for analyzing and reverse engineering hive files.

This commit is not of general interest.  It contains the tools which
I used to reverse engineer the hive format and to test changes.
Keeping these with the rest of the code is useful in case in future
we encounter a hive file that we fail to modify.

Note that the tools are not compiled by default.  You have to compile
each explicitly with:

  make -C hivex/tools <toolname>.opt

You will also need ocaml-extlib-devel and ocaml-bitstring-devel.