Add Atari DVG visualizer

The DVG format, used for vector games like Asteroids, is the
predecessor to the AVG graphics used in games like Battlezone.

Also, added some extended error checks on wireframe vertices.

Also, minor edits to the README and daily tips.

README.md

@@ -146,10 +146,11 @@ that .NET apps don't work under WINE, so it can only be run on a full
 Windows system emulation.
 
 (SourceGen versions 1.0 and 1.1 used the WinForms API, which has been
-implemented for Mono, but after encountering significant bugs that I wasn't
-able to work around I abandoned the approach and switched to WPF.  Besides
-working better under Windows, WPF uses a more modern approach (XAML) that
-may ease the transition to a cross-platform GUI API like Avalonia.)
+implemented for [Mono](https://www.mono-project.com/), but after
+encountering significant bugs that I wasn't able to work around I
+abandoned the approach and switched to WPF.  Besides working better
+under Windows, WPF uses a more modern approach (XAML) that may ease
+the transition to a cross-platform GUI API like Avalonia or MAUI.)
 
 
 ## Getting Started ##