Add Decoder::open, deprecate new

tests/decode_planes.rs

@@ -10,8 +10,9 @@ fn read_all_planes() {
     let path = PathBuf::from(TEST_IMAGE_DIR).join("planar-rgb-u8.tif");
     let file = File::open(path).unwrap();
     let io = std::io::BufReader::new(file);
+    let mut tif = Decoder::open(io).unwrap();
 
-    let mut tif = Decoder::new(io).unwrap();
+    tif.next_image().unwrap();
     let layout = tif.image_buffer_layout().unwrap();
     assert_eq!(layout.planes, 3);
     let plane_stride = layout.plane_stride.map_or(0, |x| x.get());
@@ -36,8 +37,9 @@ fn read_first_coding_unit() {
     let path = PathBuf::from(TEST_IMAGE_DIR).join("planar-rgb-u8.tif");
     let file = File::open(path).unwrap();
     let io = std::io::BufReader::new(file);
+    let mut tif = Decoder::open(io).unwrap();
 
-    let mut tif = Decoder::new(io).unwrap();
+    tif.next_image().unwrap();
     let layout = tif.image_coding_unit_layout(TiffCodingUnit(0)).unwrap();
 
     assert_eq!(layout.planes, 3);
@@ -85,12 +87,13 @@ fn read_planes_by_limits() {
     let mut buffer = DecodingResult::U8(vec![]);
 
     // Make room for 1 plane.
-    let mut tif = Decoder::new(io).unwrap();
+    let mut tif = Decoder::open(io).unwrap();
     tif = tif.with_limits({
         limits.decoding_buffer_size = 374 * 499;
         limits.clone()
     });
 
+    tif.next_image().unwrap();
     tif.read_image_to_buffer(&mut buffer).unwrap();
     assert_eq!(buffer.as_buffer(0).byte_len(), 374 * 499);