Update to 0.3.0.

Header location and library names changed, so bump API version.
No users in pkgsrc (yet).

Changes in GEGL 0.3.0
---------------------

• Improvements to thread safety and parallelism.
• Lower overhead graph travesal due from rewrite of visitors
• OpenCL support now enabled by default when detected.
• Experimental multithreading, enable by setting
  GEGL_THREADS=<number of threads> in the environment.
• Experimental mipmap rendering, which permits transparent rendering of
  previews on smaller sized versions, enable by setting
  GEGL_MIPMAP_RENDERING=true in the environment.
• Operations:
  • new operations: alien-map, antialias, apply-lens, bilateral-filter,
    bump.map, cartoon, channel-mixer, color-enhance, color-exchange,
    color-reduction, color-rotate, convolution-matrix, copy-buffer, cubism,
    deinterlace, diffraction-patterns, distance-transform, displace, edge,
    emboss, engrave, exposure, fractal-trace, high-pass, image-compare,
    illusion, invert-gamma, lens-flare, linear, linear-gradient, mosaic,
    motion-blur-circular, motion-blur-zoom, noise-cell noise-cie-lch,
    noise-hsv, noise-hurl, noise-pick, noise-rgb, noise-simplex, noise-spread,
    n-point deformation ops, oilify, panorama-projection, photocopy, plasma,
    radial-gradient, red-eye-removal, scale-size-keep-aspect, softglow,
    stretch-contrast, texturize-canvas, tile-glass, tile-seamless, tile-paper,
    tile, warp, whirl-pinch, wind, cache, cast-format, lcms-from-profile,
    npy-save, webp-load, webp-save, scale-ratio, scale-size, seamless-clone,
    sinus, supernova, value-propagate, video-degradation
  • reimplementation of gaussian-blur faster and more accurate
  • support for using URIs in image loaders
• Buffer:
  • New default tile backend, doing disk writes in a separate thread.

(wiz)