- create ruler subclasses for each type of ruler otherwise
  ParagraphEditor will be getting too big.
- include top and bottom margin in hover area of paragraphs
- add support for cycling backwards through the rulers
- add undo support (QTextDocument::undo(QTextCursor*) could help)
- add accessibility support
- think about a method to give instructions to the users
  (the bubble used by okular might be a good way to do this)
- remove hard-coded colors
  (use KDE theme or adjust to document/shape background?)
- add RTL support
- add linespacing support
- add more feature via the options docker
- add proper relayouting
  (the tools layouting doesn't flow around other shapes)
