Merge branch 'master' of github.com:qiniu/developer.qiniu.com
Merge pull request #46 from BluntBlade/master

添加imageView2与imageMogr2的文档。
Merge branch 'master' of github.com:BluntBlade/developer.qiniu.com
Merge branch 'master' of github.com:qiniu/developer.qiniu.com
修正对于HMAC的描述，应该是签名，而非加密。