priority-map-keyfn

[ninjudd]

I think I need priority-map-keyfn. I was wondering if there was a specific reason you left it out, and if you have any thoughts on how difficult it would be to add.

I'm happy to work on a patch adding it if you will accept it (and there isn't some better way to accomplish what I need). Specifically, I have a collection of items with ids and timestamps. I want to be able to look them up by id, but access them sequentially sorted by timestamp.

[ninjudd]

Here is a pull request #3.