Improve connection handling

* Fix login, password virtualhost and ssl in the connect method
* Change the behaviour of the "aioamqp.connect" method.
   ( if a method is named "connect" it should connect, not create something and call "start_connecting on )
* Add a from_url helper that connect using an url format 
   amqp[s]://username:password@host:port/virtual_host
* Add default for host and port value (localhost on the amqp standard port)
* Remove some print statement