Add initial solution files for Rustlings exercises and quizzes

- Created empty solution files for various exercises in strings, modules, hashmaps, options, error handling, generics, traits, lifetimes, tests, iterators, smart pointers, threads, macros, clippy, conversions, and quizzes.
- Each solution file contains a main function with a comment indicating that it will be automatically filled after completing the exercise.
- Added a README.md file to provide information about the solutions and their purpose.

exercises/06_move_semantics/move_semantics2.rs

@@ -0,0 +1,28 @@
+fn fill_vec(vec: Vec<i32>) -> Vec<i32> {
+    let mut vec = vec;
+
+    vec.push(88);
+
+    vec
+}
+
+fn main() {
+    // You can optionally experiment here.
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    // TODO: Make both vectors `vec0` and `vec1` accessible at the same time to
+    // fix the compiler error in the test.
+    #[test]
+    fn move_semantics2() {
+        let vec0 = vec![22, 44, 66];
+
+        let vec1 = fill_vec(vec0.clone());
+
+        assert_eq!(vec0, [22, 44, 66]);
+        assert_eq!(vec1, [22, 44, 66, 88]);
+    }
+}