added test for greatest common divisor (gcd) as well as corresponding functionality

src/main/py/more_advanced_calculations.py

@@ -0,0 +1,6 @@
+def gcd(a,b):
+    while a != b:
+        if a < b:
+            (a,b) = (b,a)
+        a -= b
+    return a

src/test/py/test_more_advanced_calculations.py

@@ -0,0 +1,18 @@
+import unittest
+from src.main.py.more_advanced_calculations import *
+
+
+class more_advanced_calculations(unittest.TestCase):
+    def setUp(self):
+        pass
+
+    def tearDown(self):
+        pass
+
+    def test_gcd_of_747_and_81_should_be_9(self):
+        self.assertEqual(gcd(747,81), 9)
+
+
+
+if __name__ == '__main__':
+    unittest.main()