py-flask-sqlalchemy: updated to 2.4.0

Version 2.4.0
-  Make engine configuration more flexible.
-  Address SQLAlchemy 1.3 deprecations.
-  get_or_404() and first_or_404() now accept a description
  parameter to control the 404 message.
-  Use time.perf_counter for Python 3 on Windows.
-  Drop support for Python 2.6 and 3.3.
-  Add an example of Flask's tutorial project, Flaskr, adapted for
  Flask-SQLAlchemy.

(adam)