Observing core types

[jayvdb]

I would like to have observable dicts. This seems like a pattern that notifyr
might want to provide an implementation for, and docs with a recipe for observing other core types.

I noticed that observable(dict) fails because it adds update and collections use update. It would be useful to allow the method names to be configurable, or use semi-private names / dunder names, to avoid clashes with the wrapped classes API.

If the core type needs to be subclassed in order to be observed, a mixin would be helpful.

[victorcmoura]

@jayvdb it seems to be a great feature. Thanks for the heads up, I might be trying to implement it in a couple of weeks.