Specially useful when using `path` convertors, to take a whole path as a parameter, like `/some/url/{p:path}`. PR [#234](https://github.com/tiangolo/fastapi/pull/234) by [@euri10](https://github.com/euri10).

* Make default parameter utilities exported from `fastapi` be functions instead of classes (the new functions return instances of those classes). To be able to override the return types and fix `mypy` errors in FastAPI's users' code. Applies to `Path`, `Query`, `Header`, `Cookie`,...