Flatten exports into index.ts

[tstirrat15]

Description

We made a change in #197 to support a commonjs use case. A by-product of that change was that ESM imports that reach into the module are no longer valid, because the exports key effectively restricts you from importing from any other files.

This has been noted in both #199 and #201. It's a regression in that the ergonomics of the library are now much worse - you have to get the v1 export out of the library and then reference its members, for both types and concrete objects.

The way to approach this will basically be export * from 'the/other/paths', as I understand it.