`as_declarative` has moved

[David Lord]

as_declarative has been removed from the top level module between 0.9.8 and 0.9.9. This no longer works:

from sqlalchemy.ext.declarative import as_declarative

Instead, this is required:

from sqlalchemy.ext.declarative.api import as_declarative

This seems to be an unintended change, as there's no reason for it to have been removed, and there's no mention in the changelog.

Discovered while answering this Stack Overflow question.

[Mike Bayer]

Duplicate of #3324.