* 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.
* SelfTests: Added a cEvent stress-test.
* cNetwork: Fixed startup event hang.
The original code used to hang with a ~ 1:50000 chance, because on Linux the cEvent was destroyed before its "Set()" returned.
