📦 RFC — Convert modules to ESM

[jrolfs]

Use ECMAScript modules instead of CommonJS.

• Convert all require based imports to use import
• Update build and package entry points to be backward compatible with CJS consumers

See

• https://2ality.com/2019/10/hybrid-npm-packages.html #### See
• https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c

Pure ESM Dependencies

• feat(deps): bump arrify from 2.0.1 to 3.0.0 #420
• build(deps-dev): bump slash from 3.0.0 to 4.0.0 #415
• feat(deps): bump read-pkg-up from 7.0.1 to 8.0.0 #390