warnings in msvc2015 around localtime and gmtime

[andry81]

fmt/time.h(51): warning C4996: 'localtime': This function or variable may be unsafe. Consider using localtime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.
fmt/time.h(86): warning C4996: 'gmtime': This function or variable may be unsafe. Consider using gmtime_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details.

These warnings goes spammed almost everythere in sources.

[vitaut]

Fixed in fecb2d6.