Create some empty files for GIF-Image.
"Encoder" has "encode" and "encodeAll", and "Decoder" has "decode" as their methods.
"ColorMap" is used for mapping pixels of the original image to quantized colors.
All quantizers should have "quantize" method to get an instance of "ColorMap" for quantization.
All drawer should have "draw" method, which require a color map and an image to be quantized.