Make UrlParams public

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Feature Request

Make UrlParams public.

Motivation

I want to be able to nest a router under a dynamic path (/:foo) and use a middleware to extract the value of :foo and do something with it. The middleware should then be able to remove foo from the UrlParams so that when it calls Next, the nested router only sees path parameters that it understands.

Proposal

Make UrlParams public.

Alternatives

Provide a hygenic way to nest a router under a dynamic path.