[Proposal] Decoratorsfor fields conversion
@gugadev -- That's invalid syntax.

Your example `to_base64` decorator -- do you intend that to be implemented in Python or is that a function provided by your database? Is this feature intended to be bi-directional, i.e.:

```python
with open('image-file.jpg', 'rb') as fh:
    raw_data = fh.read()

user = User()
user.photo = raw_data
user.save()  # Is the photo data converted to base64 before sending it to the database?

user_from_db = User.get(User.id == 1)
data = user.photo  # When accessing the property for reading, is the raw data returned, or base64?
```

I don't think your proposal is very well thought out.

If you're looking to apply a function to the data before writing/after reading, please check out this document:

http://docs.peewee-orm.com/en/latest/peewee/models.html#creating-a-custom-field
First, congratz to the team for your excelent work. Should be nice have the option to convert automatically a field when the ORM fetchs data or call some property. For example, this model have a BLOB field:

```python
class User(BaseModel):
    @to_base64 # this fn converts the binary to base64 on property call
    photo = BlobField()

```

When you get an user and call `.photo` property, the decorators is executed and you get the base64 representation. This could be useful when serialize a model to JSON, for example.

Could this be feasible?

Thanks for reading.