Add XHTML sanitizer

[dteviot]

So can safely do preview for default parser, need to sanitize HTML. Also, may be able to automatically fix some of the "unable to convert XXX to XHTML" errors. Needs to

• [ ] Remove all attributes that are not in a white list.
• [ ] Change tags that are not known types (to <div>?)
• [x] Invalid chars in text nodes. e.g. https://royalroadl.com/fiction/5288/how-to-avoid-death-on-a-daily-basis/chapter/69854/73-night-of-the-living-zombers has a text node holding a "Form Feed" (value 0x0c) character. (Not to be confused with line feed.)

Initial attribute white list

• For all elements
  • id
  • class
  • style
• hyperlinks
  • href
• image/svg

Note, this issue is related to Refer https://github.com/dteviot/WebToEpub/issues/118

[Synteresis]

Nice, they're adding an API for this as well.

https://wicg.github.io/sanitizer-api/