fixed OptionParser::error(), removed debug output in IndentedHelpFormatter
Implemented most of the functionality in IndentedHelpFormatter format_option and format_option_strings
Remove now useless TODO comment

Thanks to Paul Hooijenga, the indented formatter is now implemented, so
we can remove the TODO comment saying that we need to implement it.
Announce end of development.

But not the complete end of maintenance. Even though I won't be checking
the code for problems, I will still merge in any patches and pull
requests.

Signed-off-by: Gabriel Filion <lelutin@gmail.com>