Backported, durable, and portable selectors designed to replace the standard
library selectors module.

Features
* Support for all major platforms. (Linux, Mac OS, Windows)
* Support many different selectors
  - select.kqueue (BSD, Mac OS)
  - select.devpoll (Solaris)
  - select.epoll (Linux 2.5.44+)
  - select.poll (Linux, Mac OS)
  - select.select - (Linux, Mac OS, Windows)
* Support for PEP 475 (Retries system calls on interrupt)
* Support for modules which monkey-patch the standard library after import
  (like greenlet, gevent)
* Support for systems which define a selector being available but don't
  actually implement it.