code: async function hashes(files) {
    const map = new Map();
  
    await Promise.all(
      files.map(async name => {
        const data = await fs.promises.readFile(name);
  
        const h = hash(data);
        const entry = map.get(h);
        if (entry) {
          entry.names.push(name);
        } else {
          map.set(hash(data), { names: [name], data });
        }
      })
    );
    return map;
  }
docs: Computes hashes for the contents of each file given.
  
  @param {Array} of {String} full paths
  @return {Map}