Remove comments from usage section before parsing.

Hi,
       I just wanted to propose a change to allow comments in the usage section.

It's pretty useful to allow a small description of the usage pattern through a comment.

Currently, if you have something like:
"""
Usage:
              program argument1                             #Comments about usage.
"""

The parser does not recognize the comment.

The regexp substitution in formal_usage will allow comments of this style to be used in the Usage section.

thanks,
-Sravan