chore(server): setup ServerProto pieces to be deprecated

- Adds a `server-proto` feature that is added to default features.
- If `server-proto` feature is not enabled, pieces that will eventually
  be deprecated and optional will be tagged deprecated, but with a note
  about the missing `server-proto` feature.

Cargo.toml

@@ -43,7 +43,8 @@ pretty_env_logger = "0.1"
 spmc = "0.2"
 
 [features]
-default = []
+default = ["server-proto"]
 nightly = []
 raw_status = []
 compat = [ "http" ]
+server-proto = []