Add Support to findAndModify method

[b564518128]

Add support for findAndModify functionality so that a Document can be retrieved and updated in one operation.

In PyMongo and Motor, this functionality is achieved with find_one_and_delete, find_one_and_update, find_one_and_replace, find_many_and_delete, find_many_and_update and find_many_and_replace methods.

https://motor.readthedocs.io/en/stable/api-asyncio/asyncio_motor_collection.html#motor.motor_asyncio.AsyncIOMotorCollection.find_one_and_update

[b564518128]

in discussion #530 it mentioned that all changing method should return the instance. It seems that it's not the case. .inc() method that I am trying to use is still returning the update result.

I would like to see those pymongo/motor methods above implemented as they would be a quite useful tool to implement auto-incrementing document id.