Cap'n proto sockets

One way to inteact with libqaul is via the libqaul-ipc crate which implements the same API as libqaul, while tunneling all calls through a previously negotiated unix socket, using the cap'n proto IPC protocol.

The same ffi C interface as for libqaul can be used, meaning that it's possible to write a service that uses this high-performance IPC channel from nearly any language.

More docs to follow, as this is still WIP!