Update example and add shutdown function

Update future pass algorithm

Update typing

Refactor DAG execution process to be extensible

Update docstrings

Rewrite input and output data handling to make it explicit and non-transparent to the user

Fix formatting in setup.cfg

Rewrite DAG execution algorithm.

Create LICENSE

Update README.md

Update README.md

Update project structure and installation information

Allow operators with multiple parents in DAG receive a dict of all input args

Fix storage data source serialization

Implement a wrapper to get the input data inside the executed function