Auto save() dirty objects on commit
If you take a look at the testcases it shows how things are saved:

https://github.com/coleifer/peewee/blob/master/tests.py#L2702

Basic workflow should be:
- turn off autocommit
- modify a bunch of models or whatever
- call `.save()` on the models you want to save
- call `.commit()` on the database and all the saves (update/insert) will be committed

The test is showing:
1. turn off autocommit
2. save two blogs
3. open up a new connection to the same database (`new_db`)
4. using that new connection query to see if there are any blogs
5. assert that there are none
6. call commit on our original connection (`test_db`)
7. use the other connection to query again for blogs
8. assert that they are present

There is no "automatic" saving of dirty models.

Hi, to speed-up my query tasks, by default I have turned-off autocommit to False in db configuration, 
means we need to call db.commit() to commit the transaction

Found now behavior doesn't flush (save) dirty objects on commit. 
Again, in sql-alchemy we don't need explicit call object.save() as we know there's dirty objects that need to be save() automatically on commit.

``` python
try:
    othermodel.create(blablafield = 'blabla value')

    mymodel = MyModel.select().first() # hehe new stuff :D
    mymodel.somefield = 'edit the field value'  # dirty object
    # mymodel.save() # maybe explicitly required only on autocommit scheme

    db.commit()
except :
    db.rollback()
```

I'm playing with more than 4 models in one task, which changing the field value anywhere,
it's a bit difficult to catch which object should call save() on the end of procedure block since changes could be applied on several place of code block logic
