Implement a "CaptureSome" combinator

[awh]

There exist in the wild APIs such as this:

GET /v2/<name>/manifests/<reference>
GET /v2/<name>/tags/list

where <name> comprises one or more path segments. It would be nice to be able to do something like this:

"v2" :> CaptureSome "name" [String] :> "manifests" :> Capture "reference" String :> Get ...
"v2" :> CaptureSome "name" [String] :> "tags" :> "list" :> Get ...

to support them.

[awh]

Could be generalised to CaptureNM allowing the specification of optional lower/upper limits as with {n,m} constraints in regular expressions.

[jml]

I've started looking into this, taking a fairly direct approach of adding a CaptureMany combinator and CaptureManyRouter.

Both thinking about the problem independently and from looking on IRC, we seem to be moving closer to the point where we have type-level regular expressions / Kleene algebra. @phadej apparently has some ideas on this.

I think taking the Router' type and making it something more obviously Kleene-ish would be a good idea, and given other circumstances I'd love to explore it myself. However, I'd probably do that in a different issue.

[jml]

Although I have started work on this, that shouldn't prevent others from having a go. I have very little coding time these days, and so should not be relied upon.