0.9.0-alpha.2 - toy-rpc Book

# Removing `AckMode`

The `Ack` implementation wasn't particular useful under practical situations as the client would likely reconnect with a different port and would thus be treated as a new client.

As the long term goal is to switch to some protocol like AMQP (which is another project that I am currently working on), proper support for message delivery acknowledgement can be expected when that is ready.