补充了两个数据集的download

[benbijituo]

Description：简要描述这次PR的内容

Main reason: 做出这次修改的原因

Checklist 检查下面各项是否完成

Please feel free to remove inapplicable items for your PR.

• [ ] 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)
• [ ] Changes are complete (i.e. I finished coding on this PR) 修改完成才提PR
• [ ] 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/。
• [ ] Code is well-documented 注释写好，API文档会从注释中抽取
• [ ] 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

• 添加了新模型；用于句子分类的CNN，来自Yoon Kim的Convolutional Neural Networks for Sentence Classification
• 修改dataset.py中过时的和不合规则的注释 #286
• 添加对var-LSTM的测试代码

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@修改过这个文件的人 @核心开发人员

[codecov-io]

Codecov Report

Merging #228 into dev0.5.0 will increase coverage by 0.03%. The diff coverage is 33.33%.

@@             Coverage Diff              @@
##           dev0.5.0     #228      +/-   ##
============================================
+ Coverage     76.24%   76.28%   +0.03%     
============================================
  Files            81       81              
  Lines          9733     9739       +6     
============================================
+ Hits           7421     7429       +8     
+ Misses         2312     2310       -2

Impacted Files	Coverage Δ
fastNLP/io/file_utils.py	15.97% <ø> (ø)	:arrow_up:
fastNLP/io/loader/classification.py	60% <33.33%> (-0.35%)	:arrow_down:
fastNLP/io/loader/matching.py	92.82% <33.33%> (-0.82%)	:arrow_down:
fastNLP/models/biaffine_parser.py	96.07% <0%> (+2.14%)	:arrow_up:

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