修改循环队列模板，把成员数据rear改为length表示队列长度，并完成各成员函数的修改。

增加成员数据tag，原有成员数据不变，改变队空和队满的判断条件为：front rear&&tag 0表示队空；front rear&&tag 1表示队满，并完成各成员函数的修改。-Modify the circular queue template, the length of the member data to rear queue length, and complete the member function changes.

Increase the member data tag, the original members of the same data, change the team empty and full team to determine the conditions: front　　rear && tag　　0 said the team empty　front　　rear && tag　　1 said the team full, and complete the member function .