Automatically compress the log files

**Is your feature request related to a problem? Please describe.**

The log files of `dat-ssg` can become quite big over time. It would be good if it was regularly compressed to make sure that the hard-disk limit isn't exceeded.

**Describe the solution you'd like**

Once a log file exceeds a size specified in the config (with a preset default), the output/error file gets transformed into a .tar.gz file with the current time/date stamp in the name without interrupting the current process.

Start by locating dat-ssg's configuration handling and the code that writes its output and error log files. Check how a configured size threshold and default could be represented, then verify that exceeding it creates a timestamped .tar.gz archive without interrupting the current process.

Written by the indexing model from the issue text.