Rewrite the argument handling code using argparse. It allows us to get
rid of a lot of manual parsing as well as the whole help message.
In addition, it fixes a few other bugs present in the previous
implementation:
- Passing 3 or more arguments that are not values for parameters would
cause an infinite loop.
- The "--template" option was not allowed (only its short form "-t"
was).
R=mark@chromium.org, brettw@chromium.org
Review URL: https://codereview.chromium.org/336513002
git-svn-id: http://src.chromium.org/svn/trunk/src/build@277450 4ff67af0-8c30-449e-8e8b-ad334ec8d88c