Update scoring_functions.py (TheAlgorithms#2291)

* Update scoring_functions.py

We can find accuracy by manually if we are not going to use sklearn library.

* Update scoring_functions.py

* Update machine_learning/scoring_functions.py

Co-authored-by: Christian Clauss <cclauss@me.com>

Author: tanujdhiman

machine_learning/scoring_functions.py

@@ -135,3 +135,7 @@ def mbd(predict, actual):
     score = float(numerator) / denumerator * 100
 
     return score
+
+
+def manual_accuracy(predict, actual):
+    return np.mean(np.array(actual) == np.array(predict))