message: add .volume to SpacegroupCell
diff: @@ -9,9 +9,10 @@ import { SpacegroupName, TransformData, GroupData, getSpacegroupIndex, OperatorD
  import { SymmetryOperator } from '../../geometry';
  interface SpacegroupCell {
  - // zero based spacegroup number
  + /** Zero based spacegroup number */
  readonly index: number,
  readonly size: Vec3,
  + readonly volume: number,
  readonly anglesInRadians: Vec3,
  /** Transfrom cartesian -> fractional coordinates within the cell */
  readonly toFractional: Mat4,
  @@ -34,7 +35,7 @@ namespace SpacegroupCell {
  return cell.index === 0 && cell.size[0] === 1 && cell.size[1] === 1 && cell.size[1] === 1;
  }
  - // returns Zero cell if the spacegroup does not exist
  + /** Returns Zero cell if the spacegroup does not exist */
  export function create(nameOrNumber: number | string | SpacegroupName, size: Vec3, anglesInRadians: Vec3): SpacegroupCell {
  const index = getSpacegroupIndex(nameOrNumber);
  if (index < 0) {
  @@ -42,6 +43,8 @@ namespace SpacegroupCell {
  return Zero;
  }
  + const volume = size[0] * size[1] * size[2]
  +
  const alpha = anglesInRadians[0];
  const beta = anglesInRadians[1];
  const gamma = anglesInRadians[2];
  @@ -64,7 +67,7 @@ namespace SpacegroupCell {
  ]);
  const toFractional = Mat4.invert(Mat4.zero(), fromFractional)!;
  - return { index, size, anglesInRadians, toFractional, fromFractional };
  + return { index, size, volume, anglesInRadians, toFractional, fromFractional };
  }
  }
  