[Web Clipper] Replace mozilla/readability with postlight/mercury

Joplin Web Clipper currently uses Mozilla’s Readability, which in my experience, performs worse than Postlight’s Mercury.

Simplest example is this multi-page ArsTechnica article: https://arstechnica.com/information-technology/2019/11/half-an-operating-system-the-triumph-and-tragedy-of-os2/

  • Readability fails to extract all pages of the article whereas Mercury succeeds.
  • Mercury also returns the URL of the lead image, if exist.
  • In general, I got the impression that Mercury works “better” but cannot back this with a corpus or anything like that.

I would like to know what the community thinks, and hopefully start a discussion about better/other alternatives for clipping simplified page.