* #parent is confusing, as usually parent refers to the parent
  slot (also had a clash with slot)
TextBlock text fragments know their TextBlock

* and minor style adjustments
Link now knows whether it is visible through its text_block

* fixes #879
* previous commits were needed to get all of this wired up
* implication is that the visibility of a text fragment is defined
  by whether or not its parent text_block is visible
* May benefit from a more general approach
Merge pull request #888 from shoes/make-cursor-adjust-over-links

Make texts know their TextBlock and hence their visibility

* Changelog: bugfix
* fixes a regression within this version release
* wired texts up to know their TextBlock