refactor: save lot implementation and follow up refactors

rewrote qr code to match the now safe lot

src/error.rs

@@ -20,6 +20,8 @@ pub enum Error {
     Message(String),
     #[fail(display = "{:?}", _0)]
     Image(image_meta::ImageError),
+    #[fail(display = "{:?}", _0)]
+    Utf8(std::str::Utf8Error),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;
@@ -48,6 +50,12 @@ impl From<std::io::Error> for Error {
     }
 }
 
+impl From<std::str::Utf8Error> for Error {
+    fn from(err: std::str::Utf8Error) -> Error {
+        Error::Utf8(err)
+    }
+}
+
 impl From<image_meta::ImageError> for Error {
     fn from(err: image_meta::ImageError) -> Error {
         Error::Image(err)