Fix broken graphviz import 

Update introduction message in README.md and docs/index.rst 

Upgrade dependencies and update runtime configs 

Add support for another list representation, Node.equals and Node.clo… …ne methods

Refactor code for readability and conciseness 

Add type annotations 

Add changes for version 6.0.0 

Remove a setup.py classifier 

Change Node.value to Node.val and minor refactors 

Update README.rst and documentation