getReferences = async (heads, amount = 0) => {
    let refs = []
    const shouldStopTraversal = async (entry) => {
      return refs.length >= amount && amount !== -1
    }
    for await (const { hash } of traverse(heads, shouldStopTraversal)) {
      refs.push(hash)
    }
    refs = refs.slice(heads.length + 1, amount)
    return refs
  }
Get an array of references to multiple entries in the past.
@param {Array<Entry>} heads An array of Log heads starting rom which the references are collected from.
@param {number} amount The number of references to return.
@return {Array<string>}
@private