log4tango: Remove LOG4TANGO_HAVE_INT64_T with std::chrono

[t-b]

cppTango/log4tango/src/PatternLayout.cpp

Lines 202 to 220 in 1945e65

	struct MillisSinceEpochComponent : public PatternLayout::PatternComponent {
	virtual void append(std::ostringstream& out, const LoggingEvent& event) {
	#ifdef LOG4TANGO_HAVE_INT64_T
	int64_t t = event.timestamp.get_seconds() -
	TimeStamp::get_start_time().get_seconds();
	t *= 1000;
	t += event.timestamp.get_milliseconds() -
	TimeStamp::get_start_time().get_milliseconds();
	out << t;
	#else
	double t = event.timestamp.get_seconds() -
	TimeStamp::get_start_time().get_seconds();
	t *= 1000;
	t += event.timestamp.get_milliseconds() -
	TimeStamp::get_start_time().get_milliseconds();
	out << std::setiosflags(std::ios::fixed)
	<< std::setprecision(0) << t;

[mliszcz]

Hi @t-b
I see you mentioned this issue in #759 but can't see where and if you plan to address this. Thus I did a quick PR in #794. Let's see if it passes the tests. The PR changes API and ABI of LoggingEvent but I think users are not supposed to access that directly.