1. xio_context revamp - embedding the event loop entity into the context
2. ev_loop API is now deprecated.
3. dispatch default behavior comply with epoll. (default is level triggered)

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>
comments update for doxygen

Signed-off-by: Eyal Salomon <esalomon@mellanox.com>