Expose index the TapeError occured on

Signed-off-by: trivernis <trivernis@protonmail.com>

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "charred"
-version = "0.3.5"
+version = "0.3.6"
 authors = ["trivernis <trivernis@protonmail.com>"]
 edition = "2018"
 license-file = "LICENSE"

src/tapemachine.rs

@@ -10,6 +10,11 @@ impl TapeError {
     pub fn new(index: usize) -> Self {
         Self { index }
     }
+
+    /// Returns the index the error occured on
+    pub fn get_index(&self) -> usize {
+        self.index
+    }
 }
 
 impl Display for TapeError {