[zingmp3_vn] Add new extractor

[hatienl0i2612]

Please follow the guide below

• You will be asked some questions, please read them carefully and answer honestly
• Put an x into all the boxes [ ] relevant to your pull request (like that [x])
• Use Preview tab to see how your pull request will actually look like

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Before submitting a pull request make sure you have:

• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
• Searched the bugtracker for similar pull requests
• Checked the code with flake8

In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under Unlicense. Check one of the following options:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

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Description of your pull request and other information

• I see the zingmp3.py site is using an old version is mp3.zing.vn
• I have added a new extractor, zingmp3_vn.py, supporting the latest version is zingmp3.vn

[dstftw]

Read tutorial and coding conventions.

[hatienl0i2612]

I have read the tutorial, I do not know what error I have in coding conventions.

[hatienl0i2612]

i don't know where is the bug in coding conventions

[hatienl0i2612]

Can someone help me know where I have the error in coding conventions.