* Write into a single fmt::memory_buffer
* Use string_view instead of AString for listener callbacks
* Also collapsed vFLOG and vLOG functions into one per formatting type
* Replaces AppendVPrintf with fmt::sprintf
* fmt::ArgList now used as a type safe alternative to varargs.
* Removed SIZE_T_FMT compatibility macros. fmt::sprintf is fully portable and supports %zu.
* Adds FLOG functions to log with fmt's native formatting style.
Peter Bell