Deprecate unusable structs without a public constructor

Author: kornelski

src/codecs/gif.rs

@@ -68,7 +68,10 @@ impl<R: Read> GifDecoder<R> {
 }
 
 /// Wrapper struct around a `Cursor<Vec<u8>>`
+#[allow(dead_code)]
+#[deprecated]
 pub struct GifReader<R>(Cursor<Vec<u8>>, PhantomData<R>);
+#[allow(deprecated)]
 impl<R> Read for GifReader<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         self.0.read(buf)

src/codecs/tiff.rs

@@ -167,7 +167,10 @@ impl ImageError {
 }
 
 /// Wrapper struct around a `Cursor<Vec<u8>>`
+#[allow(dead_code)]
+#[deprecated]
 pub struct TiffReader<R>(Cursor<Vec<u8>>, PhantomData<R>);
+#[allow(deprecated)]
 impl<R> Read for TiffReader<R> {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         self.0.read(buf)

src/dynimage.rs

@@ -1395,6 +1395,7 @@ mod test {
         // Test that structs wrapping a DynamicImage are able to auto-derive the Default trait
         // ensures that DynamicImage implements Default (if it didn't, this would cause a compile error).
         #[derive(Default)]
+        #[allow(dead_code)]
         struct Foo {
             _image: super::DynamicImage,
         }