fmtlib: updated to 5.3.0

5.3.0:
* Introduced experimental chrono formatting support
* Added experimental support for emphasis (bold, italic, underline, strikethrough), colored output to a file stream, and improved colored formatting API
* Added support for 4-bit terminal colors
* Parameterized formatting functions on the type of the format string. Any object of type S that has an overloaded to_string_view(const S&) returning fmt::string_view can be used as a format string
* Made std::string_view work as a format string
* Added wide string support to compile-time format string checks
* Made colored print functions work with wide strings
* Introduced experimental Unicode support
* Improved locale support
* Constrained formatting functions on proper iterator types
* Added make_printf_args and make_wprintf_args functions
* Deprecated fmt::visit, parse_context, and wparse_context. Use fmt::visit_format_arg, format_parse_context, and wformat_parse_context instead.
* Removed undocumented basic_fixed_buffer which has been superseded by the iterator-based API
* Disallowed repeated leading zeros in an argument ID
* Reintroduced support for gcc 4.4
* Fixed compilation on platforms with exotic double
* Improved documentation
* Added pkgconfig support which makes it easier to consume the library from meson and other build systems

(adam)