This adds --rectify for a parent-aspect-ratio-preserving --squarify
variant, reverting squarify to try to match the aspect ratio of a
square (1:1).
I can see arguments for both of these. On one hand --squarify makes the
squarest squares, which according to Mark Bruls et al's paper on the
topic is easier visually compare. On the other hand --rectify may be
more visually pleasing and fit into parent tiles better.
d3 allows for any ratio, but at the moment I'm not seeing a strong
reason for the extra parameter.
Christopher Haster
1c92b7e892