Support Path Parameters in route specifications

[jan-g]

I've just thrown up a quick sketch of (what I think is) an efficient approach to handling (and caching routes for) path parameters. There's a basic outline plus a toy implementation here: https://github.com/jan-g/path-params

(Lemme know if you think it's worthwhile pursuing this; I think this is probably the lowest-cost approach that can deal with most "realistic" route sets.)

[zootalures]

@jan-g FWIW I have a simple proposal that refactor route storage here: #313