v0.2.19

• PATCH: new exports, with no break. The packing engine and the joint bench use the same balance and stability measures, so the contract computes them.
• balanceOf(boxes, container) gives the balance of a layout: gapCv, centroidOffset, the empty share of each side and sideRange.
• procrustesOf(base, next, { unit, rotate }) gives the move of the box centers after the best move and rotation, in units of W. perChange divides it by the change share.
• balanceMeasureSpecs(stage) gives the specs of the 9 measures with the prefix of a stage, for example pack.balance.sideRange. balanceMeasures gives the values with the same ids.
• docs/BALANCE.md gives the definitions and the reasons.