* Added support for middleware activation via IMiddlewareFactory
- IMiddlewareFactory and IMiddleware are new extensiblity points for
activating and authoring middleware. Under the covers, middleware is still
very much just a function. This just provides a nice way to get a per request
activated middleware instance that is created and released via the IMiddlewareFactory.
The caveats are that middleware needs to be registered in the container (by default)
and that not possible to explicitly pass arguments directly via UseMiddleware.
- Added tests
David Fowler