Issue #15: MERGE support added (#17)

* Issue #15: MERGE support added

* Removed vague check

Removed check
`if object:`

Author: Glitchfix

redisgraph/client.py

@@ -170,3 +170,13 @@ def delete(self):
         Deletes graph.
         """
         return self.redis_con.execute_command("GRAPH.DELETE", self.name)
+    
+    def merge(self, pattern):
+        """
+        Merge a node or relation.
+        """
+
+        query = 'MERGE '
+        query += str(pattern)
+
+        return self.query(query)