liyuqi

#5 Aggregations in 5 Minutes: The Nickel Tour of the Aggregation Framework

###Sample Document
```
mongos> db.logs.findOne()
{
	"_id" : ObjectId("556172a53004b760dde8a488"),
	"d_id" : ObjectId("556172a53004b760dde8a443"),
	"v" : 6205,
	"timestamp" : ISODate("3129-12-13T02:03:17.906Z"),