v0.6.0

Rigging quality-of-life: slice a model into a skeleton faster, place each bone's
pivot where it belongs, and bring reference art in from anywhere.

Added

• Extract a selection into a child bone — in a rig's Sculpt mode, select a
  region and "Extract to bone" carves it out of the current mesh into a new child
  bone, left exactly where it was. Its joint defaults to the centre of the cut,
  so it rotates about where it joins (a shoulder / hip). The fast way to slice a
  whole model into a skeleton.
• Edit a bone's mesh pivot in Skeleton mode — the point a bone's mesh sits on
  and rotates about is now editable while the skeleton is in view: numeric X/Y/Z
  fields + Center, or a "Move pivot" toggle to drag the mesh against its joint.
• Rotate the selection 90° — a Rotate panel turns the selected voxels a
  quarter turn clockwise or counter-clockwise about a chosen X/Y/Z axis. The
  result floats so it can be nudged into place before it settles.
• Paste a reference image from the clipboard (Ctrl+V, or the Reference
  panel button) — copy an image in a browser or any app and paste it straight in
  as a tracing guide, since a browser can't drop one onto the window.
• Scale a reference image — a Scale control sizes a guide to the model
  without re-importing it.

Fixed

• A bone's voxels could suddenly be replaced by another bone's (most visibly an
  extracted bone reverting to the one it was cut from) when the background
  autosave fired while a different bone was selected in Skeleton or Animate.