Asynchronous I/O

[Witek902]

• All file reads and writes (resources loading, log writes, game state seves, etc.) should be handled by async I/O API.
• Both Windows and Linux provide an API for that:
  • https://msdn.microsoft.com/en-us/library/windows/desktop/aa365683%28v=vs.85%29.aspx
  • http://man7.org/linux/man-pages/man7/aio.7.html

TODO:

• [ ] Extension of current FileSystem or File classes in nfCommon that will provide async read and writes.
• [ ] Write tests
• [ ] Add support for I/O dependency in AsyncThreadPool.
• [ ] Rewrite all resources reads in the engine with the new I/O API.

[mkulagowski]

As for File class for asynchronous write/read - there is one in review here