Issue with database.transaction()  for playhouse.flask_utils import FlaskDB 
You need to access the `peewee` database associated with the Flask `Database` object. So,

``` python
with database.database.transaction():
    ...
```

I am using FlaskDB

```
from flask import Flask
from playhouse.flask_utils import FlaskDB

  DATABASE = {
'name': 'testdb',
'engine': 'playhouse.pool.PooledPostgresqlExtDatabase',
'user': 'sats',
'max_connections': 32,
'stale_timeout': 600,
 }
app = Flask(__name__)
app.config.from_object(__name__)
database = FlaskDB(app)
```

How to use database.transaction()  as mentioned below
# Explicitly roll back a transaction.

```
with database.transaction() as txn:
    do_some_stuff()
    if something_bad_happened():
        # Roll back any changes made within this block.
        txn.rollback()
```

as FlaskDB has no attribute 'transaction'
