Add db connection pooling

app.py

@@ -204,3 +204,7 @@ if __name__ == '__main__':
     # Bind to PORT if defined, otherwise default to 5000.
     port = int(os.environ.get('PORT', 5000))
     app.run(host='127.0.0.1', port=port)
+
+@app.teardown_appcontext
+def teardown_db(exception):
+    db.close_conn()