add support for query parameters in Route.url_path_for

[ricardogsilva]

This PR add support for query parameters when resolving a URL with request.url_for and friends

From the added tests:

assert (
    app.url_path_for("homepage", some_query_param="this") == "/?some_query_param=this")

assert (
    app.url_path_for("homepage", **{"funky[query_param]": "this"}) =="/?funky%5Bquery_param%5D=this")

I find this useful in the context of getting a reproducible URL when generating pagination links for my API.

fixes #560

[ricardogsilva]

I'm retreating this PR since there is further activity on the issue page (#560) that suggests the starlette maintainers plan to implement this functionality as part of a deeper refactor.