This change also reset read timeout when we have sent HEADERS,
PUSH_PROMISE or DATA.

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.