combine_latest, common transformer using the base combine transformer

[frankpepermans]

No description provided.

[danschultz]

I'm thinking that maybe instead of having an additional combiner transformer, we can make the combiner arg in Combine be optional, and if it's not passed then it'll default to combining elements into a list.

[frankpepermans]

I was thinking too much in the Frappe lib mindset, which is the actual one I'm using, it would be easy to just add a _latest function there that passes a predefined function :)

[danschultz]

Ok, closing this in favor of an optional Combiner arg. I filed issue #30 here for anyone interested in tracking its progress.