http://forums.phpfreaks.com/topic/194255-curl-sending-array-as-post-value/
http://www.cnblogs.com/chy710/archive/2010/02/22/1671007.html
http://hushc.sinaapp.com/post/30.html
http://www.brandonchecketts.com/archives/array-versus-string-in-curlopt_postfields
http://www.huoxingfan.com/778.html
http://www.cnblogs.com/mingaixin/archive/2012/11/09/2763265.html