Review .npmignore settings

[calebcartwright]

Believe we've got some unnecessary bits being bundled as part of the package that is published to the registry, including renovate.json as well as the source TypeScript files and emitted JavaScript Map files.

The dev tooling files can obviously be removed, and I assume that the only *.ts file we need to ship with the package is src/index.ts though that'd need to be proven out.