0.12.0: Periodic tasks

Migrations

• https://github.com/peopledoc/procrastinate/blob/master/procrastinate/sql/migrations/delta_0.11.0_003_add_procrastinate_periodic_defers.sql

Features

• Add a periodic task (cron) system (#240)
• Add task aliases, letting you safely rename a task without loosing existing backlog (#264)

Miscellaneous

• Add py.typed to package (#272)
• Add missing documentation on arguement retry_exceptions (#271)

Kudos:

@SBillion, @elemoine, @ewjoachim and @tmartinfr