Supplying multiple URIs can simulate more real life situation on
server side.  For example, we can supply URIs of html, css and js and
benchmark the server.  The -m option is updated so that it defaults to
the number of supplied URIs.

The existing options --{read,write}-{rate,burst} are per connection.
The new options --worker-{read,write}-{rate,burst} are per worker
thread, which is overall rate limit of all connections worker handles.