group varint
https://github.com/facebook/folly/blob/master/folly/docs/GroupVarint.md
这个是facebook的实现
https://www.slideshare.net/parallellabs/building-software-systems-at-google-and-lessons-learned/48-Group_Varint_Encoding_Idea_encode
今天听说了一个压缩解压整型的方式-group-varint
原文：http://www.cnblogs.com/charlesblc/p/7193590.html
