extract-files 2.1.0 on Node.js NPM

Minor

Support browsers with >1% global usage (was >2%).
Target Node.js v6.10+ for transpilation and polyfills via package.json engines.
Support Node.js native ESM via --experimental-modules:
- Module files now have .mjs extension.
- Modular project structure that works better for native ESM.
Reduced bundle size, fixing #3:
- Using babel-preset-env to handle polyfills so only required ones are included for supported environments.
- Using Array.prototype.slice.call to convert FileList instances to arrays instead of Array.from which requires a lot of polyfills.

Updated dependencies.
Updated Prettier and ESLint config.
Prettier formats distribution code as well as source code, along with the readme and changelog.
No more source maps; Prettier does not support them.
Added a clean step to builds.
Renamed dist directory to lib.
Using Babel directly instead of Rollup.
Smarter Babel config with .babelrc.js.
Added links to readme badges.
Updated the readme support section.