feat(lib): add raw_status feature in Cargo.toml

The `RawStatus` types on the `Response` are now gone by default. To make
use of them, the `raw_status` feature must be enabled in `Cargo.toml`.

BREAKING CHANGE: To use `RawStatus`, you must enable the `raw_status`
  crate feature.

Cargo.toml

@@ -43,3 +43,4 @@ spmc = "0.2"
 [features]
 default = []
 nightly = []
+raw_status = []