Integer primary keys are expected to become AUTO_INCREMENT?
I must use PrimaryKeyField. Dooh. Sorry for being so stupid.

For the snippet:

```
class foo(peewee.Model):
    id = peewee.IntegerField(primary_key=True)

db.compiler().create_table(foo, False)
```

The SQL generated for a MySQL database was:

```
CREATE TABLE `foo` (`id` INTEGER NOT NULL PRIMARY KEY)
```

Should I expect `AUTO_INCREMENT` to be added to `id`? I may have misunderstood the docs.
