Deprecate Client#fetch

@ChristopherDavenport has been arguing for this, and I like @SystemFw’s argument about not burying use.

Steps:

1. Add @deprecated annotation to both overloads of Client.fetch.
2. Replace client.fetch(req)(f) with client.run(req).use(f) in tests and docs.

Bonus step 1.5, but more difficult: Implement a scalafix rule. Would make step 2 easier, and will help a lot of people upgrading.

[rossabaker]

@satorg It’s yours!

[rossabaker]

@kevinmeredith The problem with your IO version is leaking the response resource outside fetch. It’s equivalent to the .fetch(F.pure) or .fetch(F.delay) anti-patterns. But the Resource version is also unsafe: you’re reading the response body twice. It works when the body is created in memory, but it would fail when the response body is backed by a network socket.

@satorg I’d like to remove them, but it’s been pointed out that the client DSL still returns requests in F[Request[F]]. There was a conversation about evolving away from that as well. I think maybe those two should go together in their own PR.