For these simple tests Python's built-in unittest framework is more than enough.
No additional dependencies are required.
Added some more test cases with "special" characters to test the escaping code
better.
Some characters which could occur in a crawler's name have a special meaning in
Markdown. They are escaped to prevent them from having unintended side effects.
The escaping is only applied to the first (Name) column of the table. The rest
of the columns is expected to already be Markdown encoded in robots.json.
Improve the regular expression by removing unneeded anchors and
escaping special characters (not just space) to prevent false positives
or a misbehaving rewrite rule.
The name dark_visitors.py gives the impression that the code is entirely
related to the dark visitors website, whereas the update command relates
to dark visitors and the convert command is unrelated to dark visitors.
