Optional HTTP server to serve stats as JSON

[0xffiber]

When the async version is merged, we can leverage async architecture to run async HTTP server (optionally) to provide information about status of the attack, targets, and stats as JSON API. This is going to be a first step towards building more flexible display mechanisms (e.g HTML page to view in the browser, status bar widget, and more).

HTTP server could be launched as additional coroutine along side other tasks. The simplest HTTP endpoint would be enough even with built-in asyncio capabilities, no need to run fully fledged web framework.

Detailed discussion is required regarding the format of the output.