Refine MemorySize class

[Scienfitz]

A small refinement of the MemorySize class which renames attributes and adds the memory size in bytes (compared to the human readable format this is useful for programmatic evaluation of the mem size)

one alternative way of designing the class would be to make the *_human_readable items properties, but these are not visible when simply printing the entire memory size object

[AdrianSosic]

Hi @Scienfitz, in fact, I'd very much prefer the version you've mentioned in the PR description, with the human_readable stuff as properties. That way, we'd only have the two bytes attributes + shape attributes, and the property could return a simple tuple with the adjusted size and unit. And we can easily adjust the __str__ method if you think that's necessary.