Merge pull request #40 from BoostGSoC/async_dir_enumerate

Async dir enumerate
Now handles the lack of FILE_FS_SECTOR_SIZE_INFORMATION support on XP and Vista correctly.
Merge branch 'master' of github.com:BoostGSoC/boost.afio into more_docs_improvements
Updated to Sept WG21 mailing N3721 and N3731 papers.
Fixed breakage on GCC 4.7.