Version 0.9
-----------
- No longer wrap ``imread`` output in an ``Image`` class
- Change default value of `sigma` parameter in ``skimage.segmentation.slic``
  to 0
- ``hough_circle`` now returns a stack of arrays that are the same size as the
  input image. Set the ``full_output`` flag to True for the old behavior.

Version 0.4
-----------
- Switch mask and radius arguments for ``median_filter``

Version 0.3
-----------
- Remove ``as_grey``, ``dtype`` keyword from ImageCollection
- Remove ``dtype`` from imread
- Generalise ImageCollection to accept a load_func