Cmd currently has undocumented support for using the docstrings of 'do_' methods as the documentation for those methods.  This is a very convenient facility, except that it leads to documentation being printed with a lot of leading whitespace.

I propose to enhance the docstring support to strip the leading whitespace from the docstring, and to document this facility.  The proposed stripping algorithm is to strip a number of characters equal to the whitespace on the first non-blank line of the docstring.  This means that existing docstrings, which will typically start right after the first """, will be displayed as they were previously, but that a docstring can be formatted by starting the documentation on a new line after the """, and whitespace will be properly stripped.

Patch attached with test and documentation update.