v0.5.0

Added

• In weasysvg.portable(), a gradient with transparent stops or a fill opacity needs no soft mask. Its color stays
  one shading; the opacity becomes its level sets along the gradient, strips or rings, each painted at a constant
  opacity, within 1/64. cairo writes them as SVG gradients under clips, and Word draws the faded gradients of
  draw.io. A radial gradient whose circles do not hold each other keeps its soft mask.
• In weasysvg.portable(), a blur and a drop shadow need no soft mask: the levels of the blurred coverage
  are filled one over the other, each with a constant opacity, within 1/64 of the blur. The contours come from
  the blurred coverage of the shape (levelsets.py), and a rect takes its exact blur, at any size. cairo
  keeps them vector in a flat SVG, and Word draws the shadows of draw.io, Mermaid and blockdiag.
• A clip path that one PDF clip could not express (a <use>, several children, an even-odd child, bounding box
  units) becomes one path of all its fills, each subpath turned so that nonzero fills their union. It was an alpha
  soft mask, which Word does not draw and a printer may rasterize. Text, images, a child with a clip of its own
  and a path that crosses itself keep the soft mask. Tux and the Inkscape logo now clip without one.
• In weasysvg.portable(), the blur of a <use> of one shape takes the exact blur of that shape, in any paint:
  the glare of Tux, a shape filled with a gradient, needed a soft mask.
• In weasysvg.portable(), a mask of one gray or translucent shape is a clip to the shape and an opacity of the
  element. A mask without a white area, or empty, hides the element without a soft mask.
• The flat SVG of weasysvg-convert writes the opacity of a group as an opacity. cairo writes it as a mask of
  one rect over the whole drawing, and Word draws only some masks.

Fixed

• Clip path children that turn opposite ways unite, as in Chromium. WeasyPrint added them to one nonzero path,
  which cut a hole where they overlap.
• The flat SVG of weasysvg-convert keeps the shape of each glyph. cairo writes a glyph as its outline hinted at
  the size it is drawn: a bold label of 24 px came out wider and heavier in every viewer. The flat SVG is now
  read from a PDF eight times as large, its size still the SVG's own.
• A rect without a width or a height casts no shadow and no blur, as in Chromium: in a portable PDF its stroke
  made a dot.

Full changelog: v0.4.0...v0.5.0