fix: do not send exception trace of fatal errors to s3

When fatal error like "allowed memory exhausted" happens Syrup catches it and tries to send exception log to s3 but there does not remain enough memory for s3 client and whole script dies silently. 

So the pull request detects fatal error and prevents formatter from sending file to s3 and writes the description directly to syslog message instead. I think that in case of fatal errors it shouldn't be too long to exceed limit for syslog messages.(?) Furthermore I think it would be better to avoid this s3 communication for all fatal errors, not just memory exhaustion, because they are very serious of course and so the script should fail ASAP.