Add a meta option to allow field names renaming

[Nabellaleen]

Example is given in the README.md and in tests

It allows to implement :

class User(SQLAlchemyObjectType):
    class Meta:
        model = UserModel
        aliased_fields = {'name': 'first_name'}

To be able to have a field named first_name in your graphql schema instead of being stucked with UserModel field name name

[coveralls]

Coverage decreased (-0.4%) to 91.46% when pulling a70f254 on Nabellaleen:feature-field-name-alias into 6a96d37 on graphql-python:master.

[Nabellaleen]

Existing tests were not covering lines I've edited and I admit I don't know how to test its (I don't know what are composite fields and hybrid fields)

If someone want to help me on that, it's with pleasure ;)

[Cito]

Nice. This might be useful when you can't change the SQLAlchemy model or are using reflection.

But maybe the name "aliased_fields" is a bit misleading, because an alias is usually an alternative, additional name that exists parallel to the original name, but what you're doing is renaming the fields. Also, the other attributes use the imperative form "skip_", "use_", "exclude_", instead of "skipped_", "used_", "exclude_". So to be more clear and consistent I suggest the name "rename_fields" instead.

Btw, to answer your question above, composite fields and hybrid fields are rarely used concepts of SQLAlchemy. Composite fields allow you to pack multiple columns into one field, and hybrid attributes can act on both the instance and class level.

[Cito]

See the inline comments and the comment above regarding the name. Otherwise looks fine to me.

[jnak]

Closing this since it is now possible to rename fields via ORMField.model_attr. This will be more thoroughly documented soon. For now, you can also refer to the some of the tests.