move old files to a separate directory

old_curriculum/functions/functions5.rs

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+// functions5.rs
+// Make me compile! Scroll down for hints :)
+
+fn main() {
+    let answer = square(3);
+    println!("The answer is {}", answer);
+}
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+fn square(num: i32) -> i32 {
+    num * num;
+}
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+// This is a really common error that can be fixed by removing one character.
+// It happens because Rust distinguishes between expressions and statements: expressions return
+// a value and statements don't. We want to return a value from the `square` function, but it
+// isn't returning one right now...