Events: Break out and non-exhaust context body structs (#54)

This PR makes many of the types under `EventContext` separate `#[non_exhaustive]` structs. This makes it more feasible to add further information to connection and packet events as required in future. On this note, driver (re)connection events now include the SSRC supplied by Discord and the domain name which was connected to.

In addition, this fixes global timed events to return a list of all live tracks, and extensively details/documents events at a high level.

This was tested using `cargo make ready`.

src/events/context/data/mod.rs

@@ -0,0 +1,11 @@
+//! Types containing the main body of an [`EventContext`].
+//!
+//! [`EventContext`]: super::EventContext
+mod connect;
+mod rtcp;
+mod speaking;
+mod voice;
+
+use discortp::{rtcp::Rtcp, rtp::Rtp};
+
+pub use self::{connect::*, rtcp::*, speaking::*, voice::*};