Task
Please re-classify the V2 API documentations and make it more clear for reading.
For example:
Image OPs be classified together

p.s.
分类级别请最多设置到4级,选择这个数目是为了和官网树形展开方式相对应。
如当前：Model Configuration（1）-Evaluator（2）-Classificaition（3）-classification_error（4）

Project Background
Polish documentation of PaddlePaddle, enhancing user experience
-----Enhancement Plan:
Stage 1: https://note.youdao.com/share/?token=83F0AB634A7749E6B4676F823D6EC343&gid=69922175#/
-----Enhancement Schedule:
https://shimo.im/sheet/VnyT2IKRHjoU1a6i/6HGyl//

Thank you very much!