More flexibile customisation of cross reference text

[JimMadge]

Proposal

Spoke about this with @agoose77
Related to #168

Currently, there is some ability to customise how the visible cross reference text is created.
You can do this inline, like [Section {name}(#my-label) or in the front matter like

---
numbering:
  figure:
    template: fig (%s)
---

The templating language allows you to get (I believe) the number %s and the value of the name attribute {name}. And there are some extra options for the numbering behaviour.

It would be nice to have more flexibility in the label text creation. Perhaps allowing you to use any attribute from a node.
Related to #168, perhaps you could specify rules for a particular class of node. So, if you had a set of (team:my-team)= labels which reference to table nodes, but semantically are teams you might want just those tables to render like Team <name> rather than Table <number>.

Additional notes