links handling

[namiwang]

this is a list of issues. should be broken down into separated issues.

links in app

• external target
• internal target
  • link to other entry
    • handle link with anchor as section
  • [ ] ciatation/ref/footnotes via bottom sheet
  • [x] citing
  • [ ] footnote
  • [ ] ref link style
    • https://github.com/flutter/flutter/issues/10906
  • determine media file link

links out of app

• handle schema like wiki://, wiki-flutter://, or https://en.wikipedia.org/
  • https://github.com/flutter/flutter/issues/8727