Image API functions.
result enumeration
dmImage::RESULT_OK - = 0
dmImage::RESULT_UNSUPPORTED_FORMAT - = -1
dmImage::RESULT_IMAGE_ERROR - = -2
type enumeration
dmImage::TYPE_RGB - = 0
dmImage::TYPE_RGBA - = 1
dmImage::TYPE_LUMINANCE - = 2
dmImage::TYPE_LUMINANCE_ALPHA - = 3