[new]revised confusion class

[ROGERDJQ]

Description：代码解构，增加数据提取方法，格式化输出方法，增加元素占比计算方法

Main reason: 功能完善，代码结构调整

Checklist 检查下面各项是否完成

Please feel free to remove inapplicable items for your PR.

• [x] The PR title starts with [$CATEGORY] (例如[bugfix]修复bug，[new]添加新功能，[test]修改测试，[rm]删除旧代码)
• [x] Changes are complete (i.e. I finished coding on this PR) 修改完成才提PR
• [x] All changes have test coverage 修改的部分顺利通过测试。对于fastnlp/fastnlp/的修改，测试代码必须提供在fastnlp/test/。
• [x] Code is well-documented 注释写好，API文档会从注释中抽取
• [x] To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change 修改导致例子或tutorial有变化，请找核心开发人员

Changes: 逐项描述修改的内容

• 添加了新方法；增加数据提取方法，格式化输出方法，增加元素占比计算方法
• 代码结构调整

Mention: 找人review你的PR

@修改过这个文件的人 @核心开发人员

[codecov-io]

Codecov Report

Merging #278 into master will decrease coverage by 0.05%. The diff coverage is 80.90%.

@@            Coverage Diff             @@
##           master     #278      +/-   ##
==========================================
- Coverage   78.72%   78.66%   -0.06%     
==========================================
  Files          85       85              
  Lines       10476    10532      +56     
==========================================
+ Hits         8247     8285      +38     
- Misses       2229     2247      +18     

Impacted Files	Coverage Δ
fastNLP/core/utils.py	71.55% <80.41%> (-0.41%)	:arrow_down:
fastNLP/core/metrics.py	82.78% <84.61%> (ø)

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