Crop doesn't necessarily imply the any scaling is taking place. Several
ideas were discussed, from renaming Crop to combining both processors
into a single Resize processor (as they were in the original IK), but
those solutions were felt to either precluded future extension
(alternative resize modes) or make the API too verbose.
Removed the cache_dir, cache_filename_fields and cache_filename_format
properties of IKOptions. While these were very powerful, I felt that it was
unnecessarily confusing to have two properties (cache_dir and
cache_filename_format) that determine the filename. The new cache_to property is
modeled after ImageField's upload_to and behaves almost identically (the only
exception being that a callable value receives different arguments). In
addition, I felt that the interpolation of model properties provided by
cache_filename_fields, though useful, would be better handled by a utility
function outside of this library.
