Add Equinox.StreamId

[bartelink]

Polishes the ids -> stream name -> Decider resolution process

• removes ugly struct tuples from primary APIs (temp state from earlier performance work)

The major credit must go to @nordfjord who provided the impetus for this effort, and had the final late night insight that leaves us with a well-named and Simple mechanism that resolves all the forces in the mapping process neatly

[nordfjord]

Okay, my thinking cap has been on for a long time today so this is probably a horrible line of questioning. Given we already have a Category class, why do we not store the category name there?

[bartelink]

1. Category is needed when filtering events to react to
2. the constant would need to be passed to N Categories where a Config permits multiple stores (e.g. Memory)
3. you lose the forcing function that. makes people put the ids and the category name constant together top of file just before the events
   (and I think there are exotic situations where you'd want to parameterise the categoryName, but use a single Category instance)

[nordfjord]

This is looking great!