Please add utf-8 support for c++20

[pavel-machyniak]

It would be nice if the library would accept std::u8string and char8_t types when compiling for c++20 or higher, allowing direct interaction with utf-8 encoded unicode strings.

[vprus]

Thanks for your proposal. It probably would be nice indeed, but I'm afraid it would require someone to create a PR, since I don't have time for any feature development.