Create homework1.md
Add definitions of mapper, reducer, and combiner
Add def of supervised/unsupervised/semi-supervised
Add why not predicting tossing coin outcome
Add definition of classification/regression
Add student id, name, and align doc title center
Rename big-data-application/homework1.md to big-data-application/homework1/homework1.md
Add 2.1 code and image result
Update 2.1 title; add 2.2 code & result
Add code and img result of problem 2.3
Fix distance bug.

(matrix - a point) will provide unexpected result.
Add answer to problem cluster 1 (simulation)
Add answer to problem 2 of clustering
Merge pull request #17 from martin0258/master-big-data-homework1

Do big data course homework 1 (PR)