Writing RESTful apps is a good thing, but if you're also trying to support
web browsers, it would be nice not to be reduced to GET and POST for
everything.

This middleware allows for POST requests that pretend to be something else:
by adding either a header named X-HTTP-Method-Override to the request, or a
query parameter named x-tunneled-method to the URI, the client can say what
method it actually meant. That is, as long as it meant one of these:
    GET
    POST
    HEAD
    PUT
    DELETE
    OPTIONS
    TRACE
    CONNECT
    PATCH
If so, then the REQUEST_METHOD in the PSGI environment will be replaced
with the client's desired value. The original request method is always
stored under the plack.original_request_method key.