add epoll support

Signed-off-by: whoisz <whoisz@qq.com>
Merge branch 'master' of https://github.com/sleepwom/gdk
Merge branch 'master' of https://github.com/sleepwom/gdk
Merge branch 'master' of https://github.com/sleepwom/gdk
Merge branch 'master' of https://github.com/sleepwom/gdk
Merge branch 'master' of https://github.com/sleepwom/gdk