argument: Support multiple arguments

This will be used in future patches. Right now this should retain
similar behavior to the current argument parsing semantics. The
difference is we now require arguments to be specified only once and
error if they are specified multiple times.

Change-Id: I21e4cf9734f045c2b0991f7ed0ec6e6a569eec7d
Signed-off-by: William A. Kennington III <wak@google.com>
4 files changed