Add bindings for encoder and decoder #140

We already have bindings for roc_sender and roc_receiver (RocSender, RocReceiver in Java).

Roc Toolkit 0.3 introduced a networkless version of this API: roc_sender_encoder and roc_sender_decoder. We need to add bindings and unit tests for this new API.

Documentation for C API can be found here: https://roc-streaming.org/toolkit/docs/api/reference.html

C headers for new API are here: sender_encoder.h, receiver_decoder.h.