Finalized lens work. Started initial unit tests.

examples/effects/lens_crop_blocking.py

@@ -0,0 +1,10 @@
+from displayarray.effects import crop, lens
+from displayarray import display
+from examples.videos import test_video
+
+# Move the mouse to move where the crop is from on the original image
+
+display(test_video) \
+    .add_callback(crop.Crop()) \
+    .add_callback(lens.Barrel().enable_mouse_control()) \
+    .block()