Add web wasm to npm package

[elijahmorg]

Currently npm package is only for nodejs build. @penberg suggested that we add the limbo for web wasm to the npm package.

This should also improve the handling of the JS to use limbo. Currently there is no limbo-interface.js that can be cleanly called from the main thread. The APIs exposed in limbo-worker.js could use improvement too.

• [ ] investigate how to package both wasm binaries in the npm package
• [ ] add limbo-interface.js - something that exposes APIs in main thread
• [ ] cleanup limbo-worker.js
• [ ] add documentation on using limbo package for either nodejs or web

this is a follow on to #531 and #594