[osvxmawt] Packing many squares into many rectangles

Given a collection of squares of many different sizes and an unlimited number of rectangles of a single fixed size, pack the squares into as few rectangles as possible.

Needed for printing a collection of QR codes into a multi-page document, where each QR code represents a variable-length record.

Alternative is to concatenate the data in the QR codes, split the data into equal length chunks and reencode into equal sized QR codes, which can easily be packed densely.

Previously, packing into a single rectangle.