There's something going on with Hyper. When a 303 (see other) response is sent
in response to a POST, the browser does a GET to the location header. Hyper
somehow misreads the method parameter here, resulting in a route failer.
I need to MITM the connection to see exactly what the browser is sending and
what Hyper is receiving to see who's wrong.
Okay, so, given a URI, we can figure out which route is corresponds to.
Unfortunately, the handler is not yet part of that route, and we're not parsing
the parameters from the path quite yet. But, we're almost there!