Merge pull request #23 from micfan/master

modify logging.hpp document comments
improve file implementation.

Signed-off-by: jack <jack.wgm@gmail.com>
improve rate calc.

Signed-off-by: jack <jack.wgm@gmail.com>
revert stat calc.

Signed-off-by: jack <jack.wgm@gmail.com>
improve avhttp.log, add option AVHTTP_LOG_FILE_BUFFER/AVHTTP_LOG_FILE_NUM

Signed-off-by: jack <jack.wgm@gmail.com>