message: add InterUnitBonds.hasBond
diff: @@ -38,6 +38,11 @@ class InterUnitBonds {
  return index !== undefined ? index : -1
  }
  + /** Check if bond exists */
  + hasBond(indexA: StructureElement.UnitIndex, unitA: Unit, indexB: StructureElement.UnitIndex, unitB: Unit): boolean {
  + return this.getBondIndex(indexA, unitA, indexB, unitB) !== -1
  + }
  +
  /** Get inter-unit bond given a pair of indices and units */
  getBond(indexA: StructureElement.UnitIndex, unitA: Unit, indexB: StructureElement.UnitIndex, unitB: Unit): InterUnitBonds.Bond | undefined {
  const index = this.getBondIndex(indexA, unitA, indexB, unitB)
  