title: Impossible to insert data with PyMySQL when I use parameter
body: <p>I'm currently working on a basic query which insert data depending on the input parameters, and I'm unable to perfom it.</p>
  
  <p><code>cur.execute("INSERT INTO foo (bar1, bar2) values (?, ?)", (foo1, foo2))</code></p>
  
  <p>I have this error message:</p>
  
  <blockquote>
    <p>Exception in Tkinter callback Traceback (most recent call last):<br>
    File "/usr/lib/python3.2/tkinter/<strong>init</strong>.py", line 1426, in <strong>call</strong>
        return self.func(*args)   File "test.py", line 9, in register
        cur.execute("INSERT INTO foo (bar1, bar2) values (?,?)", (foo1, foo2))   File
    "/usr/local/lib/python3.2/dist-packages/pymysql/cursors.py", line 108,
    in execute
        query = query % escaped_args TypeError: unsupported operand type(s) for %: 'bytes' and 'tuple'</p>
  </blockquote>
  
  <p>foo1 and foo2 are both string type. I tried with <code>%s</code>, same error.</p>