Use fmt::format for loggers

[ken-matsui]

https://github.com/poac-dev/poac/blob/23471b6c352809dff0d0655cbb47586e1c8e3358/src/Logger.hpp

For error, warn, info, debug, and trace, we'd like to use fmt::format style formatting instead of std::ostream (internal implementation details). For example, the following usage is not that clear:

poac/src/main.cc

Lines 94 to 96 in 23471b6

	logger::error(
	"'poac ", *itr, "' failed with exit code `", exitCode, '`'
	);

We may want to do like this instead:

logger::error(
    "'poac {}' failed with exit code `{}`", *itr, exitCode
 ); 

We can use fmt::format for arguments to these loggers and we do, but the new interface will be clearer:

poac/src/Cmd/Build.cc

Lines 52 to 58 in 23471b6

	logger::info(
	"Compiling",
	fmt::format(
	"{} v{} ({})", packageName, getPackageVersion().toString(),
	getProjectBasePath().string()
	)
	);

logger::info can be:

logger::info( 
    "Compiling", "{} v{} ({})", packageName,
    getPackageVersion().toString(),
    getProjectBasePath().string()
);

Theoretically, error, warn, debug, and trace's function arguments would be like:

(fmt::format_string<T...> fmt, T&&... args)

And info has:

(std::string_view header, fmt::format_string<T...> fmt, T&&... args)

Note that the actual implementation may be different as to conform to the current implementation style.