feat: Add enums exercises

exercises/enums/enums1.rs

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+// enums1.rs
+// Make me compile! Scroll down for hints!
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+#[derive(Debug)]
+enum Message {
+    // TODO: define a few types of messages as used below
+}
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+fn main() {
+    println!("{:?}", Message::Quit);
+    println!("{:?}", Message::Echo);
+    println!("{:?}", Message::Move);
+    println!("{:?}", Message::ChangeColor);
+}
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+// Hint: The declaration of the enumeration type has not been defined yet.