Much renaming and refreshing of RBE

rustbyexample/variable_bindings.d/mut.rs

@@ -0,0 +1,12 @@
+fn main() {
+    let _immutable_binding = 1;
+    let mut mutable_binding = 1;
+
+    println!("Before mutation: {}", mutable_binding);
+
+    mutable_binding += 1;
+
+    println!("After mutation: {}", mutable_binding);
+
+    // _immutable_binding += 1;
+}