- help message: add a comma between the short and long option
- as doc:
- brief summary of how to invoke gas: separate [-w] [-x] on a new line as those
two options have nothing to do with the warning options.
- reordering of the warning options to have the same order as the listing.
- no-warn option description: change an "and" to a "or", as it is either the short
or long option to use, but not both at the same time.
- remove trailing whitespaces.
