[FEAT] Created the renderId method, used for cache invalidation in CCC.
[FEAT] Added pv.Mark#instanceState method, that obtains/creates the state object of a given scene instance. Used for storing extra scene-instance info, beside properties, but with less name-collision danger.
[FEAT] Added pv.Text.measureWidth.
[FIX] In pv.Text.measure, now all the text size affecting style attributes have defaults specified, avoiding that style inheritance affects the measurement.
[OPT] Several small optimizations.