v0.13.0: Release 0.13.0: charts, guide lesson 14, and the agent notes for them.

Charts: axes, number lines, function plots and bars, all following
animated ranges.

Added

• Axes::new() is a plotting box with a grid, axes, ticks and labels.
  .x_range(-5.0..5.0) and .y_range(-2.0..2.0) set the data ranges,
  .width() and .height() the box, .no_grid() drops the grid.
  axes.x_range() is a signal of Interval, so
  axes.x_range().to(-10.0..10.0, 1.0) zooms; ticks stay on round steps
  and each label keeps its value while the range slides.
• axes.plot(|x| x.sin()) draws a function as a Plot. It is sampled
  again every frame, finer where it bends, broken at jumps (no line across
  the gaps of tan) and cut at the box. .stroke(Accent) and .width(4.0)
  style it, .draw_on() draws it, and plot.to_fn(|x| x.cos(), 1.0)
  morphs it into another function.
• axes.point_on(&plot, x) keeps a dot on the curve at a signal x.
  axes.c2p(x, y) gives the scene point of a data point, and
  axes.place(node, x, y) keeps a node there.
• axes.bars([3.0, 7.5]) draws bars with their values above them;
  bars.value(0).to(9.0, 1.0) grows one, .labels(["a", "b"]) names them.
  axes.line_series(..) and axes.scatter(..) draw data points.
• NumberLine::new(0.0..10.0) is a single axis with the same methods.
• Guide lesson 14 (charts) and the charts example.

Fixed

• A long BulletList row ran off both edges of the frame. Rows now wrap
  inside 70 % of the frame width, start right of the mark, and take the
  height they need. Short lists look as before.
• check pointed at the component's own source for nodes a component
  adds. It now names the line of your add call.