message: Add width()/height() to DynamicImage
  All variants implement width()/height() naturally and there are
  situations where you want to know the size of the image without first
  converting it and without having to manually handle all variants.
diff: @@ -715,6 +715,20 @@ impl DynamicImage {
  }
  }
  + /// Returns the width of the underlying image
  + pub fn width(&self) -> u32 {
  + dynamic_map!(*self, ref p -> {
  + p.width()
  + })
  + }
  +
  + /// Returns the height of the underlying image
  + pub fn height(&self) -> u32 {
  + dynamic_map!(*self, ref p -> {
  + p.height()
  + })
  + }
  +
  /// Return a grayscale version of this image.
  pub fn grayscale(&self) -> DynamicImage {
  match *self {
  