sys/log, fs/fcb: Add support for trailers per entry in logs for fcb#3400

vrahane merged 2 commits intoapache:masterapache/mynewt-core:masterfrom

vrahane:vipul/logging_num_entries_callbacksvrahane/incubator-mynewt-core:vipul/logging_num_entries_callbacksCopy head branch name to clipboard