change avhttp.cpp to multi_download_test.cpp

Signed-off-by: Jack <jack.wgm@gmail.com>
add sync_proxy_test.cpp

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

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