The webtoons extractor can extract episode and entire comic (all
episodes) from webtoons.com.
All the logic of the extractors should be trivial except for a couple
of kludges needed:
- `ageGatePass' cookie is always set to avoid possible redirect and stop of
extraction, especially in the comic extractor
- The image URLs returned by the episode extractor could not be fetched
directly and the `Referer:' HTTP header needs to be passed to fetch them
Close#593.
39cd389679