Question: ability to implicitly select joined model instance
It seems pretty straightforward to me:

``` python
In [15]: with assert_query_count(1):
   ....:     q = User.select(User, Group).join(Group)
   ....:     for user in q:
   ....:         print user.username, user.group.name
   ....: 
... prints users and groups ...
```

Given two tables

``` python
class User(Model):
    ...

class Group(Model):
    user = FK(User)
```

and database contains

``` python
user1 = User()
group1 = Group(user=user1)
group2 = Group(user=user1)
```

Is there any way to select group related instance (resolved automatically if any) as a part of `selection`?

``` python
for user in User.select().join(Group):
    print user.group
```

I know model aliases are used differently but I imagine this could be something like `User.select(Group.alias('group')).join(Group)`
