Updated cppformat to version 86a7d856fa03fb5ba96f1a27907a4b7171f42e56 and remove spdlog::details namespace from it's source

Under linux, use the much faster CLOCK_REALTIME_COARSE clock by default (SPDLOG_CLOCK_COARSE is defined in common.h)

coarse clock, short log level

respect user-set compiler name

what if my clang compiler is not clang but clang-3.5?

discard policies on queue overflow