improve avhttp, add missing header file

Signed-off-by: Jack <jack.wgm@gmail.com>
add missing system_error.hpp

Signed-off-by: Jack <jack.wgm@gmail.com>
修正命名, 统一风格.

Signed-off-by: Jack <jack.wgm@gmail.com>
Merge branch 'master' of github.com:avplayer/avhttp
Merge pull request #3 from avplayer/master

合并最新版本