Connection notifications

[silviucpp]

Hello,

It will be nice to have at the pool level some sort of notifications sent when there is no connection or at least one connection like : connection_down, connection_up.

What I'm trying to fix:

When the server is stopped and there are log of pending requests (which I'm retrying till succeed), I can watch the connectivity status and don't send them until there is at least one buoy process connected.

This way I can improve the behavior of the app when the server where I'm sending the requests is down

A similar feature is available in gun http client as well.

Silviu