Allow `Basis` objects to take a scalar input instead of tuple for size

[janden]

Since these are all required to be square anyhow, it would be useful to have a shorthand of a scalar size that corresponds to that square.

[chris-langfield]

Since size is currently the required argument for creating a Basis, it would still have to be supplied even if we added a shortcut (let's say we called it L).

There isn't a plan to support expanding rectangular images in one of these bases, right? I would propose to just ditch the tuple and always supply an integer