Module build/resolution and TS issues

[lvlte]

Hey, I'm using double.js as a dev dependency for testing this module. It works great, except that it needs some tweaks to be usable with typescript. Since the package hasn't been updated for a while I'm creating this issue to suggest a major upgrade, that would address the following :

• Improve module build and resolution (ESM/CJS, emit declaration file for typescript and intellisense)
• Fix typescript issues
  • hi/lo props need to be definitely assigned in the constructor
  • method argument types and return types need to match the implementation
• Remove or update outdated dev dependencies
• Change the behavior of static methods (see Make static methods accept and return a tuple #94 , mention it here because it would be a breaking change, hence the "major" upgrade)