v0.2.1

Two rendering bugs, both of which made a correctly imported deck look wrong, and
the ts-pptx 4 upgrade. Nothing about the model or the editable surface changes,
so a document rendered by 0.2.0 still parses.

Fixed

• A group no longer offsets its children twice. Every grouped shape was drawn
  at twice its distance from the origin, because the renderer put the group's own
  translate on the wrapper and then rendered the children against the slide.
  The further a group sat from the origin the further its contents left it: a row
  of KPI cards across a slide ends up with some cards off the slide and the rest
  on top of the body text. The model has always said a child's placement is
  slide-absolute and that a renderer "never composes a transform"; this makes the
  renderer obey it. A table keeps its own transform, because unlike a group it is
  what its cells are positioned against.

• Percentage line spacing is written as the multiple it is. A paragraph asking
  for 105% got lines 16.8px apart whatever size its text was, so a large title
  painted its lines on top of each other. PowerPoint's spcPct is a multiple of
  each line's own font size; a CSS percentage resolves once, against the
  paragraph, before the runs inherit it, and the size lives on the runs. It is
  unitless now, which is what the inherited-spacing branch beside it already did
  and for the same stated reason. An exact spcPts spacing still emits px.

Changed

• Requires @shbernal/ts-pptx 4. The read model consolidated every colour
  onto one ColorRef, renamed Part.bytes to Part.originalBytes, and made
  importSlide refuse a source page whose hyperlink leaves the set being
  imported. Nothing here renders differently for it. Two recorded forms move
  because upstream now reads more than it did: the coverage baseline gains
  text.color.inherited on the two corpus decks that build their text as
  paragraph arrays, and the canonical model gains company.