change NEEDS_RESULT_CALLBACK to accept closures

This resolves issue #2.
This is a breaking change, and should necessitate moving to v0.3.0

FIXES: #2

src/multi/qrcode/detector/multi_detector.rs

@@ -45,7 +45,7 @@ impl<'a> MultiDetector<'_> {
         let resultPointCallback = if let Some(DecodeHintValue::NeedResultPointCallback(cb)) =
             hints.get(&DecodeHintType::NEED_RESULT_POINT_CALLBACK)
         {
-            Some(*cb)
+            Some(cb.clone())
         } else {
             None
         };