In describe.describe(), skip non-Table items
In describe.describe(), skip non-Table items

If an item in the scanned module was not something that mapper() could handle
and was not a Table object, the `entity` variable would never be defined and
the `if entity not in entries:` line would fail with

    UnboundLocalError: local variable 'entity' referenced before assignment

I ran across this when my model module contained

    Base = declarative_base()

and describe() wasn't sure what to do with it.

andras-tim/sadisplay