实现renderer.php中的mystatistics()方法

[sunner]

主要是统计当前用户（$USER）在oj中的所有表现，比如判过几次题、通过率多少、杯具过多少等等。如果你是oj的学生用户，你会知道该统计什么的。

Mainly to count all the performance of the current user ($USER) in oj, such as the number of questions, the rate of passing, the number of cups, and so on. If you are a student user of oj, you will know what the statistics are.