Added DestructionExecutor
Added static function files to wrap up the printing
Removed boost optional, the startup is used as time for the last
execution without executing the callback
Printing with threadid to show process/thread
Fixed doxygen file comments
Reformatted
Added getLogFileName()
Removed ~Files because we do not print there anymore
Printing into log file filestatistics.log if the environment does not
contain FILESTATISTICS_LOG
Documented new FILESTATISTICS_LOG feature