title: Discord.py delete all messages except pin messages
body: <p>Currently my discord bot has a feature when a person types !delete it deletes most text in the channel. However, it deletes all messages including pinned one. How can I enhance my code so that it does not delete pin messages?</p>
  
  <pre><code>if message.content.startswith('!delete'):
     tmp = await client.send_message(message.channel, 'Clearing messages...')
     async for msg in client.logs_from(message.channel):
       await client.delete_message(msg)
  </code></pre>