v0.8.0

- Breaking!! Bump min Joplin version to 2.4.0
  - This update uses some newish features of Joplin and as such requires
  all users to have Joplin 2.4.0 and above
- fix: Remove Code block background highlighting
- feat: Add line highlighting for blockquotes
  - This makes it possible to have blockquotes with a vertical bar
- chore: remove usage of cm-search-marker in favour of cm-rm-highlight
  - Most users won't notice a difference, but those that customized the
  colour might