MapReduce

參考paper：https://pdos.csail.mit.edu/6.824/papers/mapreduce.pdf

Lab 1

Part 1

1. 完成sequential implementation
    1.1 function that divides up the output of a map task（doMap() function in common_map.go）
    1.2 function that gathers all the inputs for a reduce task（doReduce() function in common_reduce.go）

2. 測試方法
    2.1 set debugEnabled = true in common.go
    2.2 cd 6.824/src/mapreduce; go test -v -run Sequential