Cross-platform and major safety update!

Recommended for all users, especially those who need macOS/Linux support.

Changelog

For both C and C++ versions:
- Added cross-platform support for restoring standard streams.
- Changed all functions to static inline, improving header safety in multi-file projects while keeping objects in each source file independent.
For the C++ version cfs.hpp:
- Added support for passing nullptr to the cfs function in C++11 and later. Its usage is the same as NULL, and NULL remains fully compatible.
For the C version cfs.h:
- Added a C99 or later standard check.

Cross-platform standard stream restoration is designed for restoring the system terminal, including environments such as CLion Terminal.
Some IDE-managed run consoles may not provide a real terminal device, so the restoration feature may not work as expected in those environments.
Since standards earlier than C99 are rarely used today, including this header in a C project below C99 will now produce a compile-time error. Please switch to C99 or later, or use an older version of cfs, such as V1.2.0.

推荐所有用户（特别是需要 macOS/Linux 支持的用户）更新

C 与 C++ 版本。
- 添加跨平台标准流恢复支持。
- 所有函数统一改为 static inline，提升多源文件项目中的头文件安全性，同时保持每个源文件中的对象相互独立。
对于 C++ 版本 cfs.hpp。
- 对于 C++11 及以上标准，添加了 cfs 函数参数中对 nullptr 的支持，用法与 NULL 相同且兼容 NULL。
对于 C 版本 cfs.h。
- 添加 C99 及以上标准检查。

跨平台标准流恢复功能适用于恢复系统终端，也包括 Clion Terminal 等。但某些 IDE 托管的运行控制台可能不提供真实终端设备，因此目前可能无法实现相应效果。
考虑到 C99 以下标准使用人数少，现在 C99 以下版本包含本头文件将会报错，请切换到 C99 及以上版本或使用旧版 cfs 如 V1.2.0