Updating `argparse_utils` module.

Adding `SmartHelpFormatter` class which overrides the
`argparse.HelpFormatter._split_lines` method to allow customizable line breaks
in the help string if the help message starts with "r|".

Also adding `get_sort_index_help_message` function to return the (very long)
help message for the sort index option.
Updating sort index option in scripts.

Making the default sort index 0 in both `dmc.py` and `dmc_plot_stats.py`
scripts. Also, adding a more informative help message for this argument in both
scripts. Lastly, updating the version numbers of both scripts due to the change
in defaults.
Appending doc string for `dmc_prob_shared_divergence.py`.

Adding note that this script is deprecated.
Updating version to 0.2.0 in `setup.py`.