Use _MiddlewareFactory as decorator with arguments

[ryd994]

This change allows _MiddlewareFactory to be used as decorator with argument:

@wsgify.middleware
def restrict_ip(req, app, ips):
    if req.remote_addr not in ips:
        raise webob.exc.HTTPForbidden('Bad IP: %s' % req.remote_addr)
    return app

@restrict_ip(ips=['127.0.0.1'])
@wsgify
def app(req):
      return 'hi'

[mmerickel]

@renyidong Could you update this PR with a test case showing your intended workflow? I think the idea itself is fine!

[ryd994]

@mmerickel Taking the example from http://docs.webob.org/en/latest/api/dec.html

@wsgify.middleware
def restrict_ip(req, app, ips):
    if req.remote_addr not in ips:
        raise webob.exc.HTTPForbidden('Bad IP: %s' % req.remote_addr)
    return app

@wsgify
def app(req):
    return 'hi'

wrapped = restrict_ip(app, ips=['127.0.0.1'])

I have to define an extra function and wrap it with the middleware.

With this patch, I would be able to achieve same effect as the example at very beginning.

[mmerickel]

@renyidong I understand the patch. I was asking if you could please add a test case to the codebase to ensure this keeps working in the future.

[ryd994]

@mmerickel Apologies for my misinterpret. I appended test code to test_middleware(). Or you would prefer adding a separate test?

[digitalresistor]

A separate test would be preferred. Thanks!

[ryd994]

@bertjwregeer Let me know if there is anything else you need.

[mmerickel]

LGTM!

[digitalresistor]

Sorry for taking so long! I've merged this into master.