If a fiber becomes ready on a user-defined event, schedule it
in the same event loop, not in the next loop, to save one epoll_wait()
invocation in cases when something is added to a fiber channel,
and there is a fiber ready for execution waiting on the channel.

Add a micro-bench to the unit test suite.

Conflicts:
	doc/sphinx/book/configuration.rst
	doc/sphinx/book/connectors/__python.rst
	doc/sphinx/book/connectors/index.rst

Change fiber_sleep(0) implementation to use fiber_wakeup().
Implement a more fair scheduling for "ready" fibers: they are
scheduled in the next event loop iteration, not in the same.

Fix a bug with readchunk returning more than was requested.

Fix mistype in load_cfg.lua (local variables)

socket.tcp_server() is the owner of all connected sockets. API users must not
close sockets inside handler() callback.