Removed unused functions and make InvalidChunkIndex a UsageError

src/error.rs

@@ -56,7 +56,6 @@ pub enum TiffFormatError {
         actual_samples: usize,
         required_samples: usize,
     },
-    InvalidChunkIndex(usize),
     InvalidTag,
     InvalidTagValueType(Tag),
     RequiredTagNotFound(Tag),
@@ -101,7 +100,6 @@ impl fmt::Display for TiffFormatError {
                     actual_samples, required_samples
                 )
             }
-            InvalidChunkIndex(index) => write!(fmt, "Image chunk index ({}) requested.", index),
             InvalidTag => write!(fmt, "Image contains invalid tag."),
             InvalidTagValueType(ref tag) => {
                 write!(fmt, "Tag `{:?}` did not have the expected value type.", tag)
@@ -207,6 +205,7 @@ impl fmt::Display for TiffUnsupportedError {
 #[derive(Debug)]
 pub enum UsageError {
     InvalidChunkType(ChunkType, ChunkType),
+    InvalidChunkIndex(usize),
 }
 
 impl fmt::Display for UsageError {
@@ -220,6 +219,7 @@ impl fmt::Display for UsageError {
                     expected, actual
                 )
             }
+            InvalidChunkIndex(index) => write!(fmt, "Image chunk index ({}) requested.", index),
         }
     }
 }
@@ -292,6 +292,12 @@ impl From<TiffUnsupportedError> for TiffError {
     }
 }
 
+impl From<UsageError> for TiffError {
+    fn from(err: UsageError) -> TiffError {
+        TiffError::UsageError(err)
+    }
+}
+
 impl From<std::num::TryFromIntError> for TiffError {
     fn from(_err: std::num::TryFromIntError) -> TiffError {
         TiffError::IntSizeError