Add buffered transport

[vykulakov]

Buffered transport, in general, reduces the number of packets that should be sent over the network because it may join many small writes to the network layer to a single big write operation. As a result, we will get better network performance in some cases.

The main important case where buffered transport will help a lot is using data compression. The compression layer generates many small writes to the network layer to send headers, checksums and so on and it ends up in many additional network packets. So buffered layer will join all those additional packets in a single one in most cases.