add logging to plugin example, improve swap, and add some consts

examples/plugin-for-example/src/main.rs

@@ -1,5 +1,6 @@
 extern "C" {
     fn it_works() -> i32;
+    fn initialize();
 }
 
 #[no_mangle]
@@ -9,4 +10,6 @@ pub fn plugin_entrypoint(n: i32) -> i32 {
     result + n
 }
 
-pub fn main() {}
+pub fn main() {
+    unsafe { initialize() };
+}