Some of the collections inside `MessageReader` were created with `new()`
instead of `with_capacity()` call. This patch fixes that or comments why
it was not done in some places.
I've decided that it would be a good idea to separete
compoments that transform text messages into byte chunks to send to
Unreal Engine and back. This means that each of them will have only one
responsibility and using them will be easier in case we decide to read
and write via tcp/ip in separate threads. The only interesting to them
both parameter is the amount of bytes that were confirmed to be received
from the Unreal Engine side, which can be easily shared "by hand".
This patch implements "reader" that accepts byte stream expected from
the game server and converts it into:
1. separate string messages;
2. amount of bytes game server reported to already have received.
