Add possibility to specify host, port and scheme with single url string

`self.mq =  IronMQ(cloud="http://localhost:8080", token="b9d0JtGlCdvD7jn9V8pk", project_id="54508d98daa0966ace000003", api_version=3)`

the same as 

`self.mq =  IronMQ(token="b9d0JtGlCdvD7jn9V8pk", project_id="54508d98daa0966ace000003", api_version=3, protocol="http", host="localhost", port=8080)`