[cbaecker]

Slight improvement to logger. Pass arguments as const-ref to prevent copying.

Enforcer calls LogPrint() in various locations, e.g. in the loop iterating the policy. This creates a copy every time.

casbin-cpp/casbin/enforcer.cpp

Lines 104 to 105 in 0ad64a7

	for (auto& p_vals : p_policy ) {
	casbin::LogUtil::LogPrint("Policy Rule: ", p_vals);

LogPrint() itself passes arguments to an instance of DefaultLogger, which takes another copy.

casbin-cpp/include/casbin/log/default_logger.h

Line 22 in 0ad64a7

void Print(std::string format, Object... objects) {

Internal logger is a no-op and copy elision may help, but i was still able to measure slight performance improvement.
Copies should be avoided unless required, e.g. for asynchronous processing.

This may affect existing implementations of the abstract Logger-class.