v0.0.4

Documentation, environment refactoring, SPCTSP and more!

• Add initial documentation on ReadTheDocs #80
• Major refactoring of environments: new subclasses (get_action_mask, check_solution_validity) and more modular operations such as get_tour_length, move the base class and utils under common/
• New SPCTSP environment
• Fix SDVRP, refactor as subclass of CVRP
• Fix OP with major refactoring; typos @eltociear
• Add Slack chat links
• Add paper link and citation
• Move dev status to Beta (it was production stable - we wish it was! Perhaps in the future... 🤞🏼)
• Misc bug fixes