ClientFlag MULTI_STATEMENTS

[q kaiwei]

I checked documents, but can't found sample codes of executing multi statements using mysql-connector-python, so need help to correct the following.

```
import mysql.connector
from mysql.connector import ClientFlag

# Connect with the MySQL Server
con = mysql.connector.connect(**CFG)
con.set_client_flags([ClientFlag.MULTI_STATEMENTS])
con.reconnect()

cur = con.cursor()

SQL = "update class set age=123 where name='w1';update class set age=456 where name='w2';"
cur.execute(SQL)

....
```