Consider alternate rendering backends

[dhleong]

JLine still doesn't actually support 24-bit true color (in fact, its conversion from RGB ANSI to their internal AttributedStyle seems broken—it's what our conversion from FlavorableCharSequence to their AttributedString for rendering is based on, and the results (from a branch for #90) are garbage:

vs this, using their Colors.roundRgbColor:

Laterna, for example, has classes to support RGB color, but it's unclear whether their abstraction will round down on terminals that don't support it....

[dhleong]

Just did an experiment and Lanterna does not automatically round down RGB to a supported color, so we'd need a translation layer that can respect the terminal's capabilities....