use this_thread::sleep_for on Windows

[kejxu]

usleep is not available on Windows, replace it with this_thread::sleep_for (available since c++11)

also a minor indentation update in include/realtime_tools/realtime_publisher.h, converted existing tabs to spaces

[mathias-luedtke]

Thanks!
Why did you keep usleep? For melodic we can switch to std::chrono right away.

[kejxu]

Why did you keep usleep? For melodic we can switch to std::chrono right away.

we are keeping usleep just so it would not change the existing behavior on Linux, will remove the macro guard and apply this change to both Linux and Windows