message: remove set_palette; change type of get_palette
diff: @@ -1015,13 +1015,8 @@ impl<R: Read + Seek> BmpDecoder<R> {
  }
  /// Get the palette that is embedded in the BMP image, if any.
  - pub fn get_palette(&self) -> &Option<Vec<[u8; 3]>> {
  - &self.palette
  - }
  -
  - /// Set the palette that will be used to decode the BMP image.
  - pub fn set_palette(&mut self, palette: Option<Vec<[u8; 3]>>) {
  - self.palette = palette;
  + pub fn get_palette(&self) -> Option<&[[u8; 3]]> {
  + self.palette.as_ref().map(|vec| &vec[..])
  }
  fn num_channels(&self) -> usize {
  