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.

solutions/12_options/options3.rs

@@ -0,0 +1,27 @@
+#[derive(Debug)]
+struct Point {
+    x: i32,
+    y: i32,
+}
+
+fn main() {
+    let optional_point = Some(Point { x: 100, y: 200 });
+
+    // Solution 1: Matching over the `Option` (not `&Option`) but without moving
+    // out of the `Some` variant.
+    match optional_point {
+        Some(ref p) => println!("Coordinates are {},{}", p.x, p.y),
+        //   ^^^ added
+        _ => panic!("No match!"),
+    }
+
+    // Solution 2: Matching over a reference (`&Option`) by added `&` before
+    // `optional_point`.
+    match &optional_point {
+        //^ added
+        Some(p) => println!("Coordinates are {},{}", p.x, p.y),
+        _ => panic!("No match!"),
+    }
+
+    println!("{optional_point:?}");
+}