Unable to chain factory.onCreate

[hellowodl]

In order to clean up my subscriptions in a way that's as clean as possible, I'd like to be able to chain factory.onCreate.

Currently this is impossible to do.
The factory.onCreate will always be the only function that gets called in the stack.

[mfellner]

Thanks for the issue!

Chaining onCreate currently doesn’t work as expected and leads to previously added callbacks being replaced.

This is because the factory stores only a single callback instead of an array.

Should be pretty easy to implement. Feel free to send a PR, or I’ll try to get it done when I have some time.