参考资料：
http://liluo.org/blog/2011/01/python-using-xlrd-xlwt-operate-excel/
http://www.cnblogs.com/BeginMan/p/3657805.html
http://suzy8802.blog.163.com/blog/static/2124020642013125521073/
http://blog.csdn.net/b_h_l/article/details/17001395
http://jingyan.baidu.com/article/5bbb5a1b3a6a1313eba1792b.html
