message: Add GELF tags for high precision time
  _timestamp_ns gives time in nanosecond resolution for better time based sorting. Also add _log_id that can be used to detect dropped UDP packets
diff: @@ -116,7 +116,12 @@ namespace fc
  gelf_message["host"] = my->cfg.host;
  gelf_message["short_message"] = format_string(message.get_format(), message.get_data());
  - gelf_message["timestamp"] = context.get_timestamp().time_since_epoch().count() / 1000000.;
  + const auto time_ns = context.get_timestamp().time_since_epoch().count();
  + gelf_message["timestamp"] = time_ns / 1000000.;
  + gelf_message["_timestamp_ns"] = time_ns;
  +
  + static unsigned long gelf_log_counter;
  + gelf_message["_log_id"] = fc::to_string(++gelf_log_counter);
  switch (context.get_log_level())
  {
  