apsw driver rejecting datetime object
```
Python version: 2.7.9
Sqlite version: 3.9.2

peewee==2.7.3
apsw==3.9.2-r1


```
 You need to use the `DateTimeField` object from the `apsw_ext` module.

``` python
from playhouse.apsw_ext import DateTimeField
```

I have a model that looks like this:

``` python
class Log(Model):
    name = CharField()
    platform = CharField(null=True)
    language = CharField(null=True)
    created = DateTimeField(default=datetime.datetime.now)
```

When I try to insert a new record

``` python
Log.create(name=agent.name, platform=agent.platform, language=agent.language)
```

I get the following error:

``` bash
File "/Users/rlander/.pythonbrew/venvs/Python-2.7.9/app/lib/python2.7/site-packages/playhouse/apsw_ext.py", line 95, in _execute_sql
    cursor.execute(sql, params or ())
TypeError: Bad binding argument type supplied - argument #7: type datetime.datetime
```

When I remove the "created" field from the Log class or use the default sqlite driver, I get no errors.
