vellumwidget 0.2.0

vellumwidget 0.2.0

Interaction-depth release (ROADMAP §4).

• Rich tooltips. Tooltip text now renders as safe HTML: an author-built
  tooltip = (e.g. via glue()) may use <b>/<i>/<br> for bold/italic/
  line breaks. Data values are escaped and only inert, attribute-free tags are
  honoured — no scripts, handlers, or attributes (no XSS). New
  as_widget(tooltip_style =) themes the tooltip box (background/color/fontsize/
  max_width).
• Touch + keyboard. The widget is driven by pointer events, so pan/brush/
  hover work with mouse, touch, and pen from one path; a two-finger pinch
  zooms. With the widget focused, arrow keys pan, +/- zoom, and 0 resets.
• Configurable export. as_widget(export_filename =, export_scale =) set the
  download filename base and a hi-res PNG multiplier; exports capture the current
  (zoomed/panned) view. A "copy PNG to clipboard" toolbar button appears where
  the Clipboard API is available.
• Large-N performance. Hover/selection highlighting uses a per-render
  key→node cache instead of a querySelectorAll per key, and the nearest-mark
  hover scan is throttled to one per animation frame.
• New "Interactive widgets: a tour" article.

Deferred: a spatial index for hit-testing (the DOM cost was the real bottleneck,
now cached; bbox scans are cheap and datashade collapses huge clouds to a
raster); coordinated zoom across linked widgets and URL deep-linking; PDF export.