Also:
- Reanamed foo and bar subcommand methods to base_foo and base_bar

History changes:
- Unknown commands are no longer saved in the history
- history command now has a -t option to generate a transcript based on commands in the history

Also:
- Moved examples transcripts from examples to examples/transcripts
- Added a new transcript for use with the pirate.py example

Modified the do_help() method to behave differently for methods which have been decorated with an argparse ArgumentParser.
This is so that help will properly deal with sub-command help.

Suppose you have a base command "base" which has two sub-commands, "foo" and "bar".  Then "help base" will provide very different help text than "help base foo".

Slightly tweaked the two argparse decorators to set an attribute in the decorated function's dictionary so that the do_help method can know which functions have an ArgumentParser and which do not.

Added a "subcommands.py" example for demonstrating how to create and use subcommands based on argparse and the cmd2 @with_argument_parser decorator.

I eliminated a few "narg=1" configurations so that a single str value is returned instead of a List[str].

I also reworded some documentation which was no longer correct after the last commit which made "history command" have the same help text as "command -h" when using one of the two argparse decorators.

Now "help command_name" and "command_name -h" provide exactly the same text.

The function docstring for the "do_*" command sets and overrides the ArgumentParser "description" if the docstring is not empty.

Removed usage of and reference to attributes and commands which have now been removed.