* Added ``getFd`` procedure for retrieving the underlying
selector's FD.
* Selectors module's procedures now accept an ``int`` as well as a
``SocketHandle``.
* ReadyKey now contains the error code for Event.Error events.
* Merge upcoming async with current.
* Various improvements to selectors (mostly docs).
Two changes to highlight:
* Renamed ``setEvent`` to ``trigger``
* Reused setBlocking from nativesockets.
* Various changes/fixes to asyncdispatch after upcoming merge.
* Make some attempts to be compatible with older selectors.
* Reuse epoll module in ioselectors_epoll.
* Fix#5128, #5184.
Removed flush() procedure from ioselectors.nim
Changed methods of work with application-driven data
* Make cache switch for kqueue, update test for it.
* Fix registerProcess bug returns wrong id.
Fix tupcoming_async test to compile with upcoming again.
Change socket() as unique identifier to dup(socket) as unique identifier.
