Requests a WebSocket session for the Real-Time Messaging API.
	
	Returns a SessionMetadata object containing the information retrieved from
	the API call.

def request_session(token, url=None):
	"""
	Requests a WebSocket session for the Real-Time Messaging API.
	
	Returns a SessionMetadata object containing the information retrieved from
	the API call.
	"""
	if url is None:
		api = SlackApi()
	else:
		api = SlackApi(url)

	response = api.rtm.start(token=token)
	return SessionMetadata(response, api, token)