• add --gdlib_config_path
  
• add Image Filters: scatter, pixelate, negate, grayscale, brightness,
  contrast, color, selectiveBlur, edgeDetectQuick, gaussianBlur, emboss,
  meanRemoval, smooth, copyGaussianBlurred
  
• add palette methods: createPaletteFromTrueColor,
  neuQuant (but discouraged), colorMatch.
  
• add interpolation methods: copyScale, copyRotateInterpolated,
  interpolationMethod.
  
• add double GD::VERSION
  
• add all gd.h constants