fix coalescing tcp packets

[albertosantini]

When the pressure on the socket is high, there is not any guarantee
for one data event per packet. Indeed multiple json messages are
coalesced in one tcp packet.

We need to add a delimeter (an arbitrary '\0', compatible with C
strings, just in case) to separate the packets in valid json messages.

So we add the delimeter when the json message is stringified and we
parse the packet to split it finally in multiple json messages.

Fixes #20

[nkcmr]

@albertosantini LGTM. Thanks for the PR.

[albertosantini]

Thanks a lot for the quick merge and for publishing a new release.

In another PR I will try to add a test.
Then I would like to refactor the code to encapsulate the delimeter.
Stay tuned. :)

[albertosantini]

Just a feedback. :)

As you know I have been using flic in Argo, an open source trading platform.

Just tested 1.3.6 with very high tick frequency mixed with order transactions: it works very well.

Now the order and the trade transactions are correctly caught: before fixing issue 20, one transaction message was lost in the space. The provider updated the streaming API and the transaction events were fired very quickly: suddenly I got that issue (and it was a show stopper).

As a nice side effect, also the quote ticks are caught correctly: before fixing issue 20, I saw a few invalid data messages, but I didn't care because tick frequency is very high and if a few tickets are lost, in my use case, is not a serious problem.