handle TCP fragmentation

[SkeLLLa]

This PR for handling TCP packet fragmentation. It defines simple protocol with header and data.
Format:

const HEADER_START = '\u0001';
const DATA_START = '\u0002';
const DATA_END = '\u0003';
const PACKET_END = '\u0004';
const HEADER_DELIMITER = '/';

Message:
<HEADER_START>
<id><HEADER_DELIMITER><method><HEADER_DELIMITER><data length><HEADER_DELIMITER><format><HEADER_DELIMITER><error>
<DATA_START>
<data_bytes>
<DATA_END>
<PACKET_END>

This protocol is needed to handle situations when TCP protocol divide long message into smaller parts to fit MTU.

@SomeoneWeird as for current version of tcp-transport, the new one covers 100% functionality + fragmentation handling. But if it's necessary we can modify protocol to handle true binary data (now it can handle only binary data that doesn't contain any protocol characters). If binary transport is needed, then protocol should be slightly different - with fixed-length header places for metadata. This will lead to maximum data size limit (because we'll have limited number of bytes for data length in header).

PS: Do not rush to merge this PR. Depending on decision on previous question the code could be simplified a bit or rewritten.

[SomeoneWeird]

I'd rather not invent our own protocol. Can we use msgpack or something?

[SkeLLLa]

@SomeoneWeird msgpack doesn't handle tcp fragmentation. It just like JSON, but smaller. You still should separate one packet from another and that's why it will also need some kind of packet separator (and this is also "own protocol"). But as msgpack transmitting buffers it will need fixed-length header that will store information about packet data size.