Derive Clone trait for Value and Field.

src/tiff.rs

@@ -99,7 +99,7 @@ impl IfdEntry {
 }
 
 /// A TIFF field.
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub struct Field {
     /// The tag of this field.
     pub tag: Tag,

src/value.rs

@@ -29,7 +29,7 @@ use std::fmt;
 use crate::endian::Endian;
 
 /// Types and values of TIFF fields (for Exif attributes).
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum Value {
     /// Vector of 8-bit unsigned integers.
     Byte(Vec<u8>),