optimzed short-TTL server connections

- e.g. for HTTP/1.0 requests with small input/output content
- such connections won't subscribe to socket/poll/epoll unless they need it for complex requests
- such connections won't register themselves to the internal connections list
- call optimized accept4() to minimize OS calls on Linux
- other optimizations and refactoring
- refreshed samples

Author: Arnaud Bouchez