hyperlog 介绍
hyperlog 基于链接和日志进行传播。
示例：
var hyperlog = require('hyperlog')
var log = hyperlog(db) // where db is a levelup instance
// add a node with value 'hello' and no links
log.add(null, 'hello', function(err, node) {
console.log('inserted node', node)
// insert 'world' with a link back to the above node
log.add([node.key], 'world', function(err, node) {
console.log('inserted new node', node)
})
})