Replace `hoards_dir` with `data_dir`

Current behavior is inconsistent. Passing a `--hoards-root <path>` on the CLI will affect where files get backed up/restored from, but not where history files are stored. They are intended to be stored together, so any options that modify one should modify the other as well. The easiest way to handle this is for the CLI flag to update the ENV that the `directories` library uses.