Misc:
  * Add note of caution to viewport documentation about rendering big
    things, and on using alternative approaches e.g. List
  * Consider updating editor to use smart translation similiar to list
    to enable editing of big documents

Features:
  * High priority:
    - Text wrapping (with markup)
    - Load & save attribute map to on-disk configuration (vty change
      pending: Read instance for Attr)
    - API for obtaining scrolling viewport state in EventM (will
      staleness be an issue here?)
  * Low priority:
    - Deal with multi-column characters everywhere

Open issues:
- Are there better or less error-prone ways of dealing with Names?
- Operations that pad widgets with fills interact with layering poorly,
depending on the user's intentions. Sometimes we want layers to be
opaque and filled, other times we want them to be transparent. How do we
deal with this in general?