Version 2.50.1

- #615: SVG2: Support a chain of uri() filters in the "filter" property
  (John Ledbetter, Sven Neumann).

- #483: Support CSS selectors for attribute matching, like rect[attr^="prefix"]

- #554: Fixed the geometry_for_layer() APIs to not ignore the passed viewport.

- Fixed CSS "import" so it allows only files from the same base directory
  (Lars Schmertmann).

- #623 - The pkg-config files (*.pc) do not define the 'svgz_supported' and
  'css_supported' variables anymore.  These variables were hardcoded
  to 'true' and unchanged since 2011.

- #624 - The source repository no longer produces a librsvg-uninstalled.pc file.