Handle send error

[biryukovmaxim]

use closure to handle fullchannel error, test checking it
resolves #27

[biryukovmaxim]

@Totodore that's a solution, but I put one todo, in case of error appears in binary payload send, will fix it when have time

[biryukovmaxim]

@Totodore Done. should we mention how many packets remaining inside of the closure?
I think it's mandatory to mention in documentation, that event is successfully delivered if there is no errors, and that resend closure can send some parts

[biryukovmaxim]

Also I added dependency to easily implement Debug for Errors including closure
Maybe It's better to implement it manually without unnecessary dependencies, isn't it?

[Totodore]

I really like the idea of the closure, I didn't considered this solution before you proposed it but it is very elegant.

[biryukovmaxim]

@Totodore in the last commit I replaced closure with Retryer struct. What do you think about that?

[Totodore]

The retryer way is better, I like it

[Totodore]

Merging

[Totodore]

One thing that it is important to note is that due to the possibility to retry to send binary packet it could lead to binary desynchronization. EngineIo binary packets have to be sent next to the event packet, so if there is a retry for a binary packet error and that between the original attempt and the retry there is another event packet sent it will break the mecanism.

[biryukovmaxim]

So I will think how to handle it. Looks like Socket should own buffer of failed messages to send them firstly or another Arc<Mutex> clone of retryer