message: add a store.rebase() description
diff: @@ -194,8 +194,18 @@ export default class Store extends Source implements Syncable, Queryable, Updata
  return this.update(reducedTransform);
  }
  -
  - rebase() {
  + /**
  + * This rebase method works similarly to a git rebase:
  + *
  + * After a store is forked, there is a parent- and a child-store.
  + * Both may be updated with transforms.
  + * If after some updates on both stores `childStore.rebase()` is called,
  + * the result on the child store will look like,
  + * as if all updates to the parent store were added first,
  + * followed by those made in the child store.
  + * This means that updates in the child store have a tendency of winning.
  + */
  + rebase(): void {
  let base = this._base;
  let forkPoint = this._forkPoint;
  