Add option to set log file save location

[egrace479]

I was surprised that the checksum CSV and log files created in my Downloads directory: /Users/john/Downloads/burress_checksums.csv and /Users/john/Downloads/burress_log.jsonl.
It would be nice to have control over where these files get written.
It also seems that these files get overwritten if run again.

Could you create an issue to determine the best location to write these log/metadata files and possibly prompt before overwriting them?

Originally posted by @johnbradley in #1 (comment)

[egrace479]

One note on this:

The log files are opened and added to as the download proceeds, so they won't be overwritten, and checksum is only created after a successful download, so it wouldn't be overwritten unless another is started with same file (i.e., batching), though it will then index everything in that folder.