Release 0.23.5

We do not yet handle all color types. This conveniently reminds us to
make the transformation into a proper animated iterator a fallible one
as adding limits later also influences this interface. In particular we
must at least remember (read: allocate) one additional frame but
potentially more. Furthermore the animation interface does yet allow the
caller to allocate target buffers.

This fits the model of e.g. emulsion better: We can query in advance if
the image is animated and can then decide to decode it as an animation
but get the pure PNG fallback if we are oblivious to the animation
capabilities just as if `png` itself did not support it. An ImageDecoder
adapter can also be added as a rather pure extra.

It's also cleaner to shift errors to actual decoding of images. We can
delay allocation of buffers until that point. The exact buffer
requirements could also depend on the dynamic information gained for the
next image which would make it hard to query limits at construction time
in any case.

Add an AnimationDecoder adaptor for APNG

Fix loss of brightness in the JPEG encoder

Update num-rational/num-complex dependency to 0.3

Some helper and interop for FlatSamples