Cross references don't work when target is a block

[mojavelinux]

Cross references don't work when the target is a block. To reproduce, assign an id to a block.

.Pretty picture
[#pretty-picture]
image::pretty-picture.png[Pretty Picture,600,400]

Then link to that block.

See the <<pretty-picture>>.

A link is created, but when you click on it, it does not work.

[mojavelinux]

We need to create destinations for every referencable block (i.e., a block with an id).

Here's the code that is needed. Perhaps we can wrap it into a utility method, create_destination.

if node.id
  dest_y = at_page_top? ? page_height : y
  add_dest node.id, (node_dest = (dest_xyz 0, dest_y))
  # optionally store this destination on the node so we can access it later
  #node.set_attr 'destination', node_dest
end

[mojavelinux]

This is a duplicate of #83.