Add a log_max_files config

[Toflar]

My log_dir stacks up log files and I only need the last few of them, I think it would be great if mage deleted the old ones for me. Locally, I can delete them manually but as soon as you start working with Jenkins and stuff, the workspace grows rather big :-)

[andres-montanez]

Hi @Toflar! A new log_limit option (defaults to 30) will be available on V5!
Thanks!