I also added documentation and integrated the tool into the testing
framework.

…ectory.

We plan to eventually install the grdata tool as a standalone command
line program. Essentially the build-system will perform some
substitutions (the CMake build system uses CMake's built-in
``configure_file`` command while the classic build system uses the
analogous ``configure_file.py`` script)

This commit introduces a few minor tweaks to grdata.py so that it can
more easily be consumed by the ``configure_file.py`` script.
- The ``configure_file.py`` script, itself, will ultimately require a
  few more tweaks so that it doesn't report occurences of python's
  decorator-syntax as errors
- However, this commit minimizes the number of required changes

Among other things, we started using picohash and using the functions in
os_utils.ch

The file registry is encoded in the autogenerated file_registry.h file
that is produced from file_registry.h.in.

To get this to work properly for the Makefile build-system, I needed to
add a new feature to ``configure_file.py``. In detail:

* ``configure_file.py`` already provided the option to replace a
  variable in a template file with multiple lines of content read from
  an external file. We assumed that this option would only be used for
  formatting multiline strings in printf statements. Consequently, the
  machinery would replace any new-line characters encountered in the
  external file with the "\n" escape-sequence used in C strings to
  represent a new-line.

* I added simply added the option to ``configure_file.py`` to do the
  same thing WITHOUT escaping new-line characters.

…ld-system

This commit makes the following changes to the CMake build system:
- it now creates the grdata executable and installs it
- it exports the program's location as a variable in grackle.pc
- it exposes the program's location through a custom CMake command
  (that custom CMake command will be revisited in future commits)

…ript

…d system.