Adds ability to specify multiple parameter names in restful urls.

Adds ability to obtain query string as a dictionary from request object.

Fix greedy matching of url root. Now _find_url_handler has to match path and params for parameterized urls.

Changed params['_param_names'] to params['_param_count']. Also made further improvements to path/param detection in _find_url_handler.

No need for this helper method to be async.

Replaced asyncio.cancel calls with task.cancel and removed unused processed_connections count. Also, self.conns[hid] = handler is now self.conns[hid] = task.