This patch moves management of received socket I/O buffers from
|DataSocketIO| into the I/O classes. Each I/O class is responsible
for (de-)allocating buffers, and consuming them once data has been
received.
All current I/O classes forward their buffers to the main thread,
but other operations are possible. For example, received data can
be parsed and processed directly in the I/O thread.
This patch renames |SocketConsumerBase| to |DataSocket|, and for the
I/O classes |SocketConsumerIO| to |DataSocketIO|. |DataSocketIO| also
contains send and receive functionality from |SocketBaseIO|.
|DataSocket| is a virtual base class that represents a socket that
transfers data, without a particular constraints to what the data
represents. |DataSocketIO| is the corresponding helper class on the
I/O thread.
