Add StreamWriter::into_inner() (#367)

This way, it's possible to retrieve the original writer after writing a
file via ZipWriter::new_stream().

Signed-off-by: Andrew Gunnerson <[email protected]>
Co-authored-by: Andrew Gunnerson <user@domain>

Author: chenxiaolong

src/write.rs

@@ -2038,6 +2038,11 @@ impl<W: Write> StreamWriter<W> {
             bytes_written: 0,
         }
     }
+
+    /// Consumes this wrapper, returning the underlying writer.
+    pub fn into_inner(self) -> W {
+        self.inner
+    }
 }
 
 impl<W: Write> Write for StreamWriter<W> {