Support for Exercises directive & Added Chinese translation (zh_CN)

[11Haoyu]

• support for exercise directive
• add translation to Chinese
• change encoding to "utf8" in the _convert.py to be compatible more languages
• translation json for exercise directive
• pre-commit runs

Co-authored-by: Ming Yang vivym@live.com

[mmcky]

thanks for this PR @11Haoyu -- I will review soon and see if we can get this merged.

[codecov-commenter]

Codecov Report

Base: 96.13% // Head: 96.17% // Increases project coverage by +0.04% :tada:

Coverage data is based on head (f43d4b9) compared to base (d37495f). Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #88 +/- ## ========================================== + Coverage 96.13% 96.17% +0.04% ========================================== Files 6 6 Lines 362 366 +4 ========================================== + Hits 348 352 +4 Misses 14 14 ``` | Flag | Coverage Δ | | |---|---|---| | pytests | `96.17% <100.00%> (+0.04%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks#carryforward-flags-in-the-pull-request-comment) to find out more. | [Impacted Files](https://codecov.io/gh/executablebooks/sphinx-proof/pull/88?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks) | Coverage Δ | | |---|---|---| | [sphinx\_proof/nodes.py](https://codecov.io/gh/executablebooks/sphinx-proof/pull/88/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks#diff-c3BoaW54X3Byb29mL25vZGVzLnB5) | `93.63% <100.00%> (+0.11%)` | :arrow_up: | | [sphinx\_proof/proof\_type.py](https://codecov.io/gh/executablebooks/sphinx-proof/pull/88/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks#diff-c3BoaW54X3Byb29mL3Byb29mX3R5cGUucHk=) | `100.00% <100.00%> (ø)` | | | [sphinx\_proof/translations/\_convert.py](https://codecov.io/gh/executablebooks/sphinx-proof/pull/88/diff?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks#diff-c3BoaW54X3Byb29mL3RyYW5zbGF0aW9ucy9fY29udmVydC5weQ==) | `93.33% <100.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=executablebooks)

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[mmcky]

@11Haoyu there are just a few pre-commit issues re: styling etc.

Running pre-commit will solve these for you locally

https://pre-commit.com