magic_arguments: dedent but otherwise preserve indentation....
magic_arguments: dedent but otherwise preserve indentation.
Previously magic_arguments stripped all whitespace at the beginning of
each line, interfering with formatting syntax which relies on indentation
to give context (e.g., code blocks). Now the docstring text is passed
through dedent to strip the global indentation before being handed off
to RawDescriptionHelpFormatter which preserves any remaining indentation.
Thanks to @rkern for suggesting the solution approach.
Closes gh-1890.
