Automatically strip `debug` in production

A bunch of small changes to reduce overall bundle size, which ultimately impacted backward compatibility.

Changed

• Remove IS_UNIQUE and DISPLAY_NAME exports in favor of $unique and $displayName keys
• Remove debug support in favor of process.env.NODE_ENV
  • This enables code stripping in production for Webpack and other bundlers and resulted in a 0.6kB bundle size reduction
• Remove hash function customization
  • As far as I know no one has used it in production and it increases scope of the package (let me know if you are!)