Freshen up Middleware docs

[danicheg]

Fixes #5086.
I did it very straightforwardly. If you have something to add, let me know.

[danicheg]

I can be biased, but explaining things using 'wrapper' doesn't help much.

[ChristopherDavenport]

I love it, theres a fix thats still needed but I like it a lot.

[ChristopherDavenport]

My wonder I've always had is what if we generally omitted the Request[F] to just call in Request docs. This is more a discussion point than something I want to see addressed here. That way when explaining it would look like Request => F[Option[Response]] which hides the noise that has to do with the internal stream bodies.

[danicheg]

I think that hiding the F type parameter is absolutely legit in docs, especially when we're explaining things using pseudo-code. And vice versa, every code snippet should be compiled and ready for copy-pasting by users.