Changes 0.2.0:
* OpenCL support
* build improvements.
* High level API to apply ops directly to buffers with arguments.
* Final bits of translation infrastructure.
* Invalidate regions when disconnecting input pads.
* Operations:
  * New operation: global-matting
  * Allow transform core to do perspective transforms.
  * Added string based key/value pairs to operations.
  * Added arguments for dealing with scaled down preview rendering.
* Added human interaction ranges and non-linear mapping to properties.
* Buffer:
  * Removed broken lanczos sampler.
  * Add gegl_buffer_set_color and gegl_buffer_set_pattern
  * Added ability to drop cached tiles.
  * Added API for handling abyss policy (not implemented yet)
  * Avoid iterating global tile cache when flushing/destroying buffers
    that have no tiles in the cache.

(adam)