* Partially port FML to Windows.

* Adds a message loop impl for Windows
* Ports `thread.cc` to Windows

All FML unittests are now passing on Windows.

FML as a whole does not compile on windows yet because `mapping.cc` imports `sys/mman.h`, which is not available on Windows and the replacement API for memory-mapped files is very different on Windows, see https://msdn.microsoft.com/en-us/library/windows/desktop/aa366556%28v=vs.85%29.aspx.

* update licenses

* review comments