Optionally use std::format in LOG4CXX_XXXX_FMT macros instead of fmt::format

[swebb2066]

This PR allows the following usage options:

1. Add -DLOG4CXX_FORMAT_NAMESPACE=std to the cmake configure step when building Log4cxx
2. Add #define LOG4CXX_FORMAT_NS std before #include <log4cxx/logger.h>

[rm5248]

Would it make sense to be able to switch this at compile time for the user? We can turn off location information by defining the preprocessor argument LOG4CXX_DISABLE_LOCATION_INFO, we could do something similar here. That can also let the user select between the two if needed, since fmt has more comprehensive options than std::format.

At least part of this could be done automatically by checking for __cpp_lib_format

[swebb2066]

Would it make sense to be able to switch this at compile time for the user?

Yes, which is done by adding #define LOG4CXX_FORMAT_NS std before #include <log4cxx/logger.h> or LOG4CXX_FORMAT_NS=std as a preprocessor argument

[rm5248]

Would it make sense to be able to switch this at compile time for the user?

Yes, which is done by adding #define LOG4CXX_FORMAT_NS std before #include <log4cxx/logger.h> or LOG4CXX_FORMAT_NS=std as a preprocessor argument

It doesn't look like it checks for that though, I think you would get a warning/error about multiple defines. I would assume it actually needs to be this:

#define LOG4CXX_USING_STD_FORMAT @LOG4CXX_USE_STANDARD_FORMAT@
#if !defined(LOG4CXX_FORMAT_NS) && LOG4CXX_USING_STD_FORMAT
#define LOG4CXX_FORMAT_NS std
#elif !defined(LOG4CXX_FORMAT_NS)
#define LOG4CXX_FORMAT_NS fmt
#endif

This information should probably also be added to the macros influencing log4cxx page.

[swebb2066]

Updated website is available for review