Expose EPOLLEXCLUSIVE

[dtolnay]

Suggestion from i.r-l.o:

EPOLLEXCLUSIVE is not exposed, which is required for some multithreading patterns.

[bobbo]

I'm guessing this looks like adding UnixReady::exclusive() and UnixReady::is_wakeup()? I can work on a patch for this.

Misunderstood the issue above, I'm still interested in working on this.

[bobbo]

Okay I've taken a look at at this. As these are Epoll specific flags, I thought it might be best to follow the unix::UnixReady pattern, so I've added a unix::EpollOpt struct, which will work with PollOpt much the same way UnixReady works with Ready. Still needs to be fleshed out, but the basic idea is shown here https://github.com/carllerche/mio/compare/master...bobbo:issue-676?expand=1. EPOLLWAKEUP (#677) can be added here too.

Would be good to get some feedback before continuing, @carllerche

[carllerche]

I hesitate to expose this flag until a deeper exploration of multi threaded polling can be done.

[carllerche]

Closing due to inactivity.