Enhancement to use model on SQLAlchemy

[gdoumenc]

I want to use swagger.model with SQLAlchemy.

In this case all properties should be defined not from init but by a callable 'resource_sqlalchemy_fields' which will return all properties.

Before doing it as a pull, I wanted to know if something was already done (I saw an old issue closed due to lack of activity) and if it is a good idea.

If so I can do a pull request...

[sobolevn]

well, yes. we are migrating for a new version. it is the current task for now, see: https://github.com/flask-restful-swagger/flask-restful-swagger/blob/version-1.0.0/flask_restful_swagger/swagger.py#L158

looking forward you PR! thanks!