Exposing lower level apis, common package

Currently, background removal is a simple and intuitive function, which is great. But I find myself needing to be a little more flexible with how I use it, and I would like to use some of the core functionality.

I noticed that none of the lower level apis are exposed and that some of the code between web and node is duplicated.

Would you be open to a pull request to create a common package that exposes the core of background removal?