Feature: API for the JS entrypoint

[fvsch]

Current package.json#main field points to lib/index.js which is empty.

It should be possible to expose the same functionality as the bin entrypoint as a function that excepts JS options, but not sure what would actually be useful here.

[fvsch]

The sirv API is pretty nice:
https://github.com/lukeed/sirv/tree/main/packages/sirv