Add fibonacci recursive implementation

Author: kolbryt

homework/fibonacci/fibonacci.hpp

@@ -12,6 +12,8 @@ int fibonacci_iterative(int sequence) {
 }
 
 int fibonacci_recursive(int sequence) {
-    // TODO: Your implementation goes here
-    return 0;
+    if (sequence == 0 || sequence == 1) {
+        return sequence;
+    }
+    return fibonacci_recursive(sequence - 1) + fibonacci_recursive(sequence - 2);
 }