v0.24.3: Merge pull request #58 from oxygenframe/release-0.24.3

Added

• code.focus_text("main", 0.4): lights one piece of the source and dims
  the rest, as focus_lines does for lines; between two pieces the
  highlight slides across, and focus_text("", 0.3) shows everything again. Explaining one expression part by part no longer needs a Txt
  per token.

Changed

• shaders::ripple() also lights the slope of each ring, so the rings show
  on a flat fill and on shaders::waves(), not only on text or an image.
  Frames with a ripple render differently.