[internal] Make Harness.output method more consistent

[slightlynybbled]

Looking at this line

For anyone who wishes to use Harness.output method directly, there is a parameter called directory. If directory is utilized, then all of the output files are not saved to the same place (.bom.tsv and .html). The workaround is use filename with an absolute path and leave directory blank.

I am happy to submit a pull request to fix this, but there are two options and I am not sure which the author wishes to engage:

Option 1. Eliminate the directory and ensure that filename is always a valid path (recommend using pathlib and making filename and instance of pathlib.Path).

Option 2. Insert directory into the .bom.tsv and .html directories.

I look forward to author's guidance on this.

[formatc1702]

In the interest of simplicity, I would go for option 1 and eliminate directory completely, since it's just as easy to include it in filename directly.

This issue is related to #60 (and indirectly, to #55); handling of file output needs some cleaning up.
If you're willing to submit a PR that fixes both issues, I'd be more than happy to include it! Any help in this regard is appreciated :)