* 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.
This was mostly done automatically and then visually inspected for obvious errors.
All //-style comments should have a 2-space separation from the code, and 1 space after the comment sign.
