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/06_move_semantics/move_semantics1.rs

@@ -0,0 +1,4 @@
+fn main() {
+    // DON'T EDIT THIS SOLUTION FILE!
+    // It will be automatically filled after you finish the exercise.
+}