Git教程参考：
系列一：
- http://boboshone.com/blog/2013/04/18/learn-git-step-by-step-1/
- http://boboshone.com/blog/2013/04/18/learn-git-step-by-step-2/
- http://boboshone.com/blog/2013/04/20/learn-git-step-by-step-3/
系列二：
- http://hi.baidu.com/sunboy_2050/item/4d492e8ae6dc835fe73d19f1
- http://blog.csdn.net/ithomer/article/details/7527877
- http://blog.csdn.net/ithomer/article/details/7529022
- http://blog.csdn.net/ithomer/article/details/7529841
系列三：
练习：
