Improve output the 'help' command.
Improve output the 'help' command.

The output of the 'help' command (added by the 'add_help_cmd' parameter)
is now more like the tree command (with three symbols and a space before
an entry).
The calculation of the index to start printing the description has also
been improved and made more reliable (it starts four spaces after the
longest command).

fmenabe/python-clg