Extract out reactive attributes

[davidbrochart]

I'm thinking about using Textual's reactive attributes in another project. From early experiments, it seems that all they need is the class holding them to have a _reactives dictionary. I don't think the event system is mandatory, except maybe if watchers are async?
How would you feel about this, since it would basically be a copy/paste of Textual's code? If you agree with that, I guess the project should mention that the reactivity stuff comes from Textual.
What about the license? I guess it must be as permissive as Textual's, e.g. MIT of BSD.

[willmcgugan]

I'm happy for you to do that.

Not sure what the MIT license says about derived works, but I'd have no issue with licensing it as MIT or BSD.

[davidbrochart]

Thanks, I created reacttrs.

[willmcgugan]

Clever name!