Deprecated for 2018.04, it's been almost a year since. Whoever is using
Magnum regularly updated already, and who not can always upgrade
gradually (2018.02, 2018.04, 2018.10, 2019.01 etc.).
It was returning either pixel size or compressed block size, which is
now available directly via other means.
This is a breaking change, but I don't expect these functions to be
used widely beyond Magnum internals.
Too much burden to implement. Nope. Sorry. All APIs were just asserting
that it's not enabled at the moment, so I may as well just remove it
completely.
Currently just does per-pixel comparison and calculates absolute delta,
failing the comparison if max/mean delta threshold is above specified
values. Useful enough for the case I have right now, might fail in other
case -- but still better than whatever else I was using before :)