This slightly modifies the HTML_TITLE_REGEX to fix two parsing errors.
The first occurred when title tags were empty (e.g. "<title></title>")
which was parsed as "</title". The second occurred when titles were a
single character (e.g. "<title>A</title>") which was not matched by the
regex, and so would fall back to link.base_url.
Now when tags are empty, it falls back to link.base_url, and single
character titles are parsed correctly.
The way the regex works now is still a bit wonky for some edge cases.
I couldn't find any cases of incorrect behavior, but it still might be
worth reworking more completely for robustness.
Most frustratingly, the outdated docker-compose link prompts users to
download an older version of the docker-compose.yml file, which packages
a broken YouTube retrieval method.
Incorrect hyphen placement in `URL_REGEX` was allowing it to match more
characters than intended. In a regex character class, a literal hyphen
can only appear as the first character in the class, or it will be
interpreted as the delimiter of a range of characters.
The issue fixed here caused the range of characters from `[$-_]`
be treated as valid URL characters, instead of the intended set of three
characters `[-_$]`. The incorrect range interpretation inadvertantly
included most ASCII punctuation, most importantly the angle brackets,
square brackets, and single quote that the expression uses
to mark the end of a match.
This causes the expression to match a URL that has a "hostname" portion
beginning with one of the intended "stop parsing" characters. For
example:
```
https://<b>www</b>.example.com/ # MATCHES but should not
https://[for example] # MATCHES but should not
scheme='https://' # MATCHES, including final quote, but should not
```
Some test cases have been added to the `URL_REGEX` assert in
archivebox.parsers to cover this possibility.
