title: Auto_increment custom Primary Key in Peewee model
body: <p>I want a primary key <code>id</code> field to be <code>Bigint</code></p>
  
  <pre><code>class Tweets(Model):
      id = BigIntegerField(primary_key=True)
      ...
  </code></pre>
  
  <p>But it needs to be auto_incremented and I can't find a way in the Peewee docs.
  Please suggest if it's possible.</p>
  
  <p>Update: I'm using MySql db.</p>