I would like lol::image to be accessible in the header-only section of
the framework, which means rethinking the locking mechanism and the way
codecs are exposed to the image class.

The containers no longer force the user to use the ptrdiff_t type for
size information. For convenience, size() now always returns an int,
and the size_s() method offers a way to handle arrays with more than
2 billion elements. Internally, we still use ptrdiff_t, though.

Since so much code had to be changed, I took the opportunity to get
rid of capitalised accessors for classes that are lowercase.

C++ containers.

of slightly overkill Image objects.

merged iteratively with our current image processing code.