hide scrollspy becasue a small problem when page scroll
css_sprite update
css sprite again
show menu_down icon
update css
update js
bind a click for menu_down icon .  add condition for shwo menu_down icon.
Merge pull request #86 from BluntBlade/master

更新Android-SDK使用文档。
upload_return修正为upload_ret（实测结果）。
Merge pull request #85 from SunLn/6708_api_nav_update

#6708 api nav update
Merge branch 'master' of github.com:qiniu/developer.qiniu.com