ANNOUNCE: graphviz-2999.16.0.0

I'm pleased to announce that I've finally tracked down all the pesky
little bugs that prevented me from releasing version 2999.16.0.0 of my
graphviz library, that helps you use the Graphviz suite of tools to
visualise graphs.

The important changes are:

* Add support for Graphviz-2.30.0:

    - New attributes:

        + `Area`
        + `Head_LP`
        + `LayerListSep`
        + `LayerSelect`
        + `Tail_LP`
        + `XLP`

    - `BgColor`, `Color` and `FillColor` now take a list of colors
      with optional weightings.

    - Layer handling now supports layer sub-ranges.

    - Added the voronoi-based option to `Overlap`.

    - Added the `Striped` and `Wedged` styles.

* Updates to attributes and their values:

    - The following attributes have had their values changed to better