0.8.0

• Breaking change: Changed CLI command format. Before: darq some_project.darq_app.darq. Now: darq -A some_project.darq_app.darq worker
• Breaking change: Scheduler (cron jobs) now run's seperate from worker (see darq scheduler command)
• Breaking change: Changed some function signatures (rename arguments)
• Breaking change: Remove redis_pool param from Darq app
• Add on_scheduler_startup and on_scheduler_shutdown callbacks