Support ES6 module loading

[dpilafian]

Add an ES6 module version of ip-range-check to prevent messages like:

WARNING in component.ts depends on 'ip-range-check'. CommonJS or AMD dependencies can
cause optimization bailouts.
For more info see: https://angular.io/guide/build#configuring-commonjs-dependencies

Maybe create an additional .js file containing lines similar to:

import { ipaddr } from 'ipaddr.js';
...
export { checkManyCidrs };

Or maybe create a /dist folder with both the CommonJS and ESM versions plus the .d.ts declaration file.

[danielcompton]

I have no strong feelings (or knowledge) about how this should be done. Happy to take a PR with whatever you think is best.