added _tornado to instance, cleanup event, afterServerStarted event

[robert-boulanger]

created cleanup event created afterServerStarted Event

[manatlan]

@robert-boulanger have you got a simple example, evolving this 2 new events, so I could figure out how to use them irl.

[robert-boulanger]

Two real world samples

def afterServerStarted(self,ws,reserved = None):
    # reserved is currently None, reserved for future use
    # here we get tornados io_loop
     loop = ws.loop
     if self.mongo_client is None:
        # and here we use the loop to pass it over to Motor, so the asyncronous DB Driver uses the same io_loop as tornado
        # this maybe use full also for other 3rd party asyncio based modules
        self.mongo_client = AsyncIOMotorClient("mongodb://localhost:27017",replicaset="MyReplicaSet", read_preference=pymongo.ReadPreference.PRIMARY,io_loop=io_loop)

def cleanup(self):
    # Close DB connection properly 
    self.mongo_client.close()