inputParser: warn for unmatched arguments

When an argument is unmatched, show a warning for the user.
This helps when a typo is made in an argument, e.g.
`stadalone` instead of `standalone`.

Also, the comment for `KeepUnmatched` was wrong:
 that parameter only determines whether Unmatched parameters
 are retained in some structure, not whether error messages are issued
Merge pull request #287 from egeerardyn/warnUnmatched

inputParser: warn for unmatched arguments