more refactoring

[jordaaash]

Continued from #5

To do

• Uncomment or remove all commented out blocks of executable code
• Refactor out clone method
• Document all public methods in more detail
• Address all remaining TODO/FIXME comments
• Revamp error types
• Colocate unit and integration tests
• Remove Makefile and use yarn scripts + shx (platform-indepedent and JS devs are more familiar with)
• Finish ES modules configuration

[jordaaash]

I ran into issues using ES modules with the example in the readme, which expects commonjs to work. It might be better to just use commonjs for now until proper build tooling is set up.