* Adding an incrementing peer ID for easier connection identification on peer disconnect

* Removing the private override of onDisconnection in http::Handler

* Adding unit test for onDisconnection

* - Exposing a peer handle from the ResponseWriter
- Making disconnection test a bit more deterministic; there appears to be a race condition between server.shutdown() returning and the onDisconnection() callback succeeding.
- Adding Active Connections info in test case to demonstrate usage.

* Reducing verbosity of test output
Co-authored-by: Ian Roddis <gitlab@ie2r.com>