Modernisation

[qntm]

• Bump major version to 2.
• Interface now uses Uint8Arrays, not ArrayBuffers.
• Move test data to dedicated test-data directory.
• Completely rewrite the package so it isn't quite so hopelessly inefficient in terms of speed or memory usage.
• Use ES6 modules now; use rollup to export all three of an ES6 module, a plain old CommonJS module and an IIFE suitable for use in the web browser. Should fix #6.