Changed the detection of with_argparse decorated commands to be less hacky/brittle.
  Now it tags the function with help_summary.
Fixed issue with handling commands that provide a custom help_ function. We can now
redirect the output to a string to be formatted with the other commands.
Added some documentation explaining the new help categories.
Updated unit tests.

In verbose help, added check for argparse usage block (starting with 'usage: '), to skip that block and move to the next comment block
Added unit tests for new categorization code
Updated example to demonstrate skipping of argparse usage statement

Reads the __doc__ for a command function and provides the first block of text for each command.
Updated help_categories.py to demonstrate a multi-line comment block for a command.

Added example of multiple commands grouped by categories