Mark enum Context and Error as non_exhaustive.

src/error.rs

@@ -30,6 +30,7 @@ use std::io;
 
 /// An error type returned when parsing Exif data.
 #[derive(Debug)]
+#[non_exhaustive]
 pub enum Error {
     /// Input data was malformed or truncated.
     InvalidFormat(&'static str),

src/tag.rs

@@ -109,6 +109,7 @@ impl fmt::Display for Tag {
 
 /// An enum that indicates how a tag number is interpreted.
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[non_exhaustive]
 pub enum Context {
     /// TIFF attributes defined in the TIFF Rev. 6.0 specification.
     Tiff,	// 0th/1st IFD (toplevel)