Copy euph-api-related parts from cove

Also includes the required dependencies and some minor changes to the
module structure, as well as all the clippy and rustc warnings.

src/api.rs

@@ -0,0 +1,13 @@
+//! Models the euphoria API at <http://api.euphoria.io/>.
+
+mod events;
+pub mod packet;
+mod room_cmds;
+mod session_cmds;
+mod types;
+
+pub use events::*;
+pub use packet::Data;
+pub use room_cmds::*;
+pub use session_cmds::*;
+pub use types::*;