Driver: Move Bitrate import out of crate root. (#53)

This is a simple organisational change which moves `crate::Bitrate` to `crate::driver::Bitrate` to slightly clean up the crate root.

This has been tested using `cargo make ready`.

src/driver/tasks/message/core.rs

@@ -1,10 +1,9 @@
 #![allow(missing_docs)]
 
 use crate::{
-    driver::{connection::error::Error, Config},
+    driver::{connection::error::Error, Bitrate, Config},
     events::EventData,
     tracks::Track,
-    Bitrate,
     ConnectionInfo,
 };
 use flume::Sender;

src/driver/tasks/message/mixer.rs

@@ -3,9 +3,8 @@
 use super::{Interconnect, UdpRxMessage, UdpTxMessage, WsMessage};
 
 use crate::{
-    driver::{Config, CryptoState},
+    driver::{Bitrate, Config, CryptoState},
     tracks::Track,
-    Bitrate,
 };
 use flume::Sender;
 use xsalsa20poly1305::XSalsa20Poly1305 as Cipher;