Adding CODE_STYLE.md and CODE_STYLE_CN.md for APISIX

[yongboy]

What this PR does / why we need it:

We missing the apisix's lua code style guide when writing a plugin, fixing the code bug.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible?

Summary

1. Adding CODE_STYLE.md base on https://github.com/apache/incubator-apisix/blob/v1.2/CODE_STYLE.md, and change it for meeting APISIX project
2. Adding CODE_STYLE_CN.md base on https://juejin.im/post/5d71f9bcf265da03b76b437c, and change it for readable :))
3. Fixing the CODE_STYLE_CN.md invalid path bug within doc/zh-cn/README.md

Issues resolved

Fix #1846

[moonming]

@yongboy

Scan detected 1 error(s) in 1 file(s):
  [./CODE_STYLE_CN.md]:
      20: line has trailing whitespace.

please fix the code style, which blocked CI.

[yongboy]

Removed line 20's trailing whitespace with the commit:
a0ae4c1

But the CI still tell me the error:

  [./CODE_STYLE_CN.md]:
      20: line has trailing whitespace.

Checking the CODE_STYLE_CN.md line 20, you can't find the trailing whitespace now:

What should I do now ?

[membphis]

works fine at my local machine. I will rerun the Github Action.

Reading configuration file [.travis/ASF-Release.cfg]...
Scanning files starting at [./]...
All checks passed.

[membphis]

@yongboy many thx