feat: Add Drop-based defer implementation

examples/defer.rs

@@ -0,0 +1,31 @@
+// Go's defer in Rust!
+
+struct Defer<F: Fn()> {
+    f: F
+}
+
+impl <F: Fn()> Drop for Defer<F> {
+    fn drop(&mut self) {
+        (self.f)()
+    }
+}
+
+// Only added this for Go-syntax familiarity ;-)
+fn  defer<F: Fn()>(f: F) -> Defer<F> {
+    Defer { f }
+}
+
+fn main() {
+    let mut i = 1;
+
+    // Calling it "token" ... could be something else. The lifetime of this
+    // controls when the action is run.
+    let _token = defer(move || println!("Value is: {}", i));
+
+    i += 1;
+    println!("Value is: {}", i);
+}
+
+// Prints:
+// Value is: 2
+// Value is: 1