For this to be possible, the function to convert a codepoint to urf8 was
moved to the header and made constexpr.
Now it's not necessary to store a std::string just to serve as a buffer
for holding this string. All the computation is done at compile time.
Clang-format sees the text behind `#pragma region` as code and formats it. Instead of stating the copyright and date there, it's now in the comment block right below it. The text "Copyright" is left in the `#pragma region` line, as clang-format sees it as a single identifier.
I took the opportunity to normalize the dates, and add the copyright notice to the source files where it was missing them (except for third-party and the generated resources.h file).
