Propagate kwargs from SessionFactory constructor to create_engine

[lincrosenbach]

Kwargs is created empty for setting up the sqlalchemy create_engine this makes impossible to someone add specific settings for creating the engine.
An alternative would be to propagate from session factory kwargs. By doing that, it should allow any user to set all possible parameters like in:
https://docs.sqlalchemy.org/en/latest/core/engines.html#engine-creation-api

Issue reference:

tornado-sqlalchemy/tornado_sqlalchemy/__init__.py

Line 135 in 6a3f82a

kwargs = {}

[siddhantgoel]

I've actually been thinking of removing the custom arguments that SessionFactory defines (hence the warning when session_events and engine_events are present) and just defining the constructor as def __init__(self, *args, **kwargs) and then passing those arguments directly to SQLAlchemy's create_engine. Thoughts?

[lincrosenbach]

I like your proposed change. It would make more flexible but maybe backward compatibility may be compromised. Any use of it with positional arguments may break the API. Let me see if our colleagues have some thoughts about it. @igorcandeia @nicoddemus @kfasolin @igortg

[nicoddemus]

I don't see much problem in breaking backward compatibility here: if you are following semantic versioning then there are no backward compatibility guarantees for 0.x versions.

[kfasolin]

I agree, since the definition on SQLAlchemy already is sqlalchemy.create_engine(*args, **kwargs) letting *args, **kwargs here makes it transparent to configure the engine the way its needed

[siddhantgoel]

Cool. I've requested an update to #78 .

[siddhantgoel]

Just merged #78 . I'll try to make another release in the next 2-3 days.

[lincrosenbach]

Solved on #78

[siddhantgoel]

Just pushed v0.6.1.