prefer fractional font metrics, for proper scaling of node size;

tuned metrics;

more explicit Layout.Info: size and content;
allow multi-line vertex label, based on content;
misc tuning;

explict layout graph structure, with dummies and coordinates;
explicit metrics for dummy box;
tuned signature;
misc tuning;

tuned metrics;

separate module Metrics;
maintain static metrics (with font) and visible_graph via layout;