Add ESM implementation and type declarations

[mherod]

Description of the Change

• Adds ESM implementation, essentially a slight syntax shuffle of the original CommonJS code
• Adds type declaration
• Update the README with new examples for the ESM code

Benefits

• Gives developers the choice of either CJS or ESM without needing their bundler to do all the work
• Type declaration enables IDE type inference, less coding in the dark

Possible Drawbacks

• Duplication of the implementation could be mitigated by transpiling from a Typescript source with a bundler setup. Easy ground for Vite to take care of if we wanted to do that.

Verification Process

Applicable Issues