feat(cfg): 添加配置文件解析

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 80.85106% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 82.45%. Comparing base (393e5e4) to head (66b64a8).

Files	Patch %	Lines
test/test_args.cc	83.33%	0 Missing and 6 partials :warning:
test/test_cfg.cc	66.66%	0 Missing and 2 partials :warning:
test/test_demo.cc	66.66%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #18 +/- ## ========================================== - Coverage 90.90% 82.45% -8.46% ========================================== Files 2 6 +4 Lines 11 57 +46 Branches 6 22 +16 ========================================== + Hits 10 47 +37 - Partials 1 10 +9 ``` | [Flag](https://app.codecov.io/gh/mengdemao/lazybsd/pull/18/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=%E5%AD%9F%E5%BE%B7%E8%8C%82) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/mengdemao/lazybsd/pull/18/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=%E5%AD%9F%E5%BE%B7%E8%8C%82) | `82.45% <80.85%> (-8.46%)` | :arrow_down: | 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=%E5%AD%9F%E5%BE%B7%E8%8C%82#carryforward-flags-in-the-pull-request-comment) to find out more.

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