single-header logging library for C++ applications

 Easylogging++ is a light-weight, high performance logging library for
 software written in C++11 and higher. It is highly configurable and
 extensible, supports both severity- and verbosity-based logging,
 provides crash handling, STL logging, integration with syslog, log
 rotation, performance-specific logging for profiling, pointcut-style
 extensions of third-party code...