code: async function copyNewerSingle(srcpath, destpath, opts) {
  
    let { interval = 1000, verbose = false } = opts
  
    let stat = await FS.stat(srcpath)
    // Stat and check the filesystem entry type.
    if (stat.isDirectory()) {
      // Directory, ensure destination exists and return.
      let made = await mkdirp(destpath)
      if (verbose && made) { console.log(`${made} - directory created`)}
      return 'dir'
    }
    else if (!stat.isFile()) {
      // Not a file.
      throw new Error("Not supported.")
    }
  
    let srcmtime = stat.mtime
    let destmtime
    try {
      // Stat destpath and get the mtime.
      destmtime = (await FS.stat(destpath)).mtime
    }
    catch (err) {
      // path does not exist
    }
  
    if (destmtime !== undefined && srcmtime - destmtime <= interval) {
      // destpath does not exist or mtime is equal, return.
      if (verbose) { console.log(`${srcpath} == ${destpath}`) }
      return false
    }
  
    // Ensure parent directory exists.
    await mkdirp(`${destpath}/..`)
  
    // Commence copying.
    let rs = FS.createReadStream(srcpath)
    let ws = FS.createWriteStream(destpath)
    rs.pipe(ws)
    await waitForStreamEnd(ws)
  
    // Set mtime to be equal to the source file.
    await FS.utimes(destpath, new Date(), stat.mtime)
  
    if (verbose) { console.log(`${srcpath} -> ${destpath}`) }
    return true
  }
docs: Copies a single file. Returns 'dir' if directory, true if successful, false if not. Throws Error if not a file and not a directory.