added in 0.2.1

(meta-middleware handler middleware-key wrap-fn)
If routing metadata is available, builds a (memoized) handler using
`(wrap-fn handler route-id metadata)` and routes the request to it.

The middleware data is expected at `[:meta :middlewares k]` of the routing
metadata attached by `wrap-routing` and the middleware itself is supposed to
be activated using `enable-middlewares`. Note that even `nil` metadata is
allowed an will be passed to `wrap-fn`.

If `wrap-fn` returns `nil`, no middleware will be applied.