Standardization fixes

[Jakz]

This pull request is aimed to refactor and beautify the code:

• removed non-standard constructs allowed by GCC compiler but not by C++ standard (eg. designated initializers, uint)
• increased utilization of some C++11/C++17 STL functions like std::clamp, std::stoi and such
• std::chrono instead of <sys/time.h>
• continued replacing POSIX like file system access functions with std::filesystem
• added build options to force windowed mode and specific resolution for debugging

[Jakz]

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