chore: setup todos

[Zubs]

This pull request adds a new TODO.md file outlining future development plans and improvements for the toRoman project. The document organizes upcoming tasks by feature area, providing a clear roadmap for enhancements.

Planned improvements and features:

Web Playground and CLI:

• Plan to create a simple web playground UI for live input/output demos and address any quirks.
• CLI enhancements, including support for operation and format flags, input piping, and more flexible commands.

Error Handling and Testing:

• Aim for consistent error design, possibly introducing a custom error class, and more comprehensive tests.

Advanced Features:

• Consider adding an expression parser for evaluating Roman numeral expressions, and implementing an immutable Roman object API.

Other Improvements:

• Plans for benchmarking, framework integrations (e.g., React, Vue), version bump to 2.1.0, and updating the README with new examples.