[WIP] Add FFI support and Rust bindings

[radu-matei]

This PR:

• adds a CGO main package that exports the Pull and Push functions
• adds the C header and a (for now Mac) shared object
• starts a simple Rust crate that consumes the shared object

TODO:

• [ ] add Push and export it from the Rust crate
• [ ] document how to generate bindings for other languages

[radu-matei]

Ultimately, the overhead to the build process, CGO, and FFi make this solution less than ideal for production scenarios.

Closing.