graphviz-2999.7.0.0: TODO

Areas to work on:

* Utilise the generic graph class once it is finalised.

* Add generic versions (that is, order isn't important) of
  Data.GraphViz.Types

* Encoding: Graphviz uses UTF-8 by default, Latin1 when set; should
  graphviz use utf8-string and disable changing the encoding?