Middleware and logging docs changes

[drewish]

I'd like to offer up some docs changes from the perspective of an experienced programmer that is very new to rust. I'm trying to use tide for a simple project to webhooks and got tripped up by a few things:

• I wanted to enable some basic logging and it seemed like an oversight that the crate's overview didn't specifically show how to use the middleware. I added a code sample to try to demonstrate that.
• I didn't realize the RequestLogger needed additional crates to actually log output so I added a couple comments there.
• I tried using the middleware example to write my own logger... and then realized that "simplified example" meant "won't compile". I found an example in the tests and realized it wasn't that much more complicated to show a working example.

[drewish]

peer_addr() doesn't seem to exist any longer and url() is not uri().

[drewish]

Looks like something timed out in that test. Not seeing a way to restart it so going to see if closing and reopening the PR will trigger it.