Remove use of Query.yield_per.

SQLAlchemy 1.0 disallows yield_per with eagerloading[1].

Fixes #143.

[1]: http://docs.sqlalchemy.org/en/rel_1_0/changelog/migration_10.html#joined-subquery-eager-loading-explicitly-disallowed-with-yield-per

pokedex/lookup.py

@@ -195,7 +195,7 @@ class PokedexLookup(object):
         for cls in self.indexed_tables.values():
             q = self.session.query(cls).order_by(cls.id)
 
-            for row in q.yield_per(5):
+            for row in q:
                 row_key = dict(table=unicode(cls.__tablename__),
                                row_id=unicode(row.id))