Expose Client Interface via FFI

[jazzz]

The Core module needs to call the client interface over FFI. This currently does not exist.

Once #71 is completed, an FFI interface should be added to allow the integration with the Core Module.

The FFI should expose all functions required for operation.

Tasks:

• enumerate required functions
• build C compatible FFI
• Verify functionality in https://github.com/logos-co/logos-chatsdk-module)

Notes

• A legacy FFI layer exists for the "core" api however should not be used as its no longer needed.
• Look at safer_ffi library to manage ffi interface.