- use namespace bracket all content in documentation to reduce useless namespace prefix.
- change the argument type of AbstractSetting and CoreManager to yycc_u8string_view instead of const yycc_char8_t*.
- throw exception if given setting name is invalid in ConfigManager, instead of slient fallback.
- rename Constrain to Constraint in code and documentation.
- remove massive annotation of encoding helper because the documentation is enough.
- fix doxygen character shift warnings.
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