feat: 增加mongo 查询功能

[jackielulu17325]

add mongo.py

关联issue: #282

[codecov]

Codecov Report

Merging #332 into master will increase coverage by 0.18%.
The diff coverage is 86.81%.

@@            Coverage Diff            @@
##           master    #332      +/-   ##
=========================================
+ Coverage   85.01%   85.2%   +0.18%     
=========================================
  Files          66      67       +1     
  Lines        8678    8747      +69     
=========================================
+ Hits         7378    7453      +75     
+ Misses       1300    1294       -6

Impacted Files	Coverage Δ
sql/models.py	94.92% <ø> (ø)	⬆️
sql/engines/__init__.py	73.8% <0%> (+18.25%)	⬆️
sql/engines/tests.py	99.77% <100%> (ø)	⬆️
sql/engines/mongo.py	82.25% <82.25%> (ø)

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[hhyo]

感谢提交，为了合并代码，还需要你帮忙完善如下信息

• 具体描述一下PR新增的功能，以及能够支持的查询语法，抑或是限制条件
• 完善新增功能的单元测试，可参考其他引擎的测试用例，https://github.com/hhyo/Archery/blob/master/sql/engines/tests.py

[LeoQuote]

我发现表结构没实现，mongo有表结构吗？

[jackielulu17325]

没有吧… 发自我的iPhone

…

------------------ Original ------------------ From: Leo Q <notifications@github.com> Date: Wed,Jul 17,2019 6:59 PM To: hhyo/Archery <Archery@noreply.github.com> Cc: Jackielulu <lujunjie@weibopay.com>, Author <author@noreply.github.com> Subject: Re: [hhyo/Archery] Archery jackie (#332)

[LeoQuote]

可能你还是要返回一个无表结构的假返回，不然可能会报错，你本地试用可用吗？

[jackielulu17325]

我这边没有报错唉

[LeoQuote]

@jackielulu17325 我帮你改了一点代码, 加了一些单元测试, 把最新拉到本地再看一下, 应该没啥问题了.
@hhyo 稍等作者确认了再合, 应该问题不大

[hhyo]

演示环境已更新