Split crate into lib.rs and main.rs

src/lib.rs

@@ -0,0 +1,11 @@
+#![cfg_attr(not(test), no_std)]
+
+pub mod serial;
+pub mod vga_buffer;
+
+pub unsafe fn exit_qemu() {
+    use x86_64::instructions::port::Port;
+
+    let mut port = Port::<u32>::new(0xf4);
+    port.write(0);
+}