Removed 'normalize_spaces', redundant operation handled by argparse.ArgumentDefaultsHelpFormatter.

Leaving the text untouched allows the use of other argparse formatter classes.  As discussed in https://github.com/rubik/mando/issues/13 with this change can use the argparse RawTextHelpFormatter formatter class like:

    from argparse import RawTextHelpFormatter
    @mando.command(formatter_class=RawTextHelpFormatter)
    def myfunction():
        '''This
           will
           format
           exactly
           the
           way
           that
           I
           want.
        '''