* Fix cast[pointer] issues on nim-devel.
* More cast[T] fixes.
* Fix compilation error.
* Add oserrno.nim
Further fixes for Windows and Linux.
* MacOS fixes.
* More Windows fixes and attempt to fix 1.2, 1.4 branches.
* Implicitly import/export oserrno.
* Replace oserrno with osdefs.
* Return back oserrno.
* epoll to oserrno.
* datagram/stream to oserrno.
* common to oserrno.
* test to oserrno.
* ioselectors_epoll() refactoring.
* ioselectors_kqueue() refactoring.
* ioselectors_poll() initial refactor.
* Remove `s.count` because it inconsistent and not used in `chronos`.
* Remove Windows version of select() engine.
* Add ability to switch event queue engine via `asyncEventEngine` command line option.
* Make it possible to switch between engines.
* Fix epoll regression.
* Fix poll() engine issues.
* Address review comments.
* Add proper trick.
* Address review comments.
* Bump version to 3.1.0.
Eugene Kabanov