Generate a class map file
array|string $dirs Directories or a single path to search in:
string $file The name of the class map file:
public static function dump($dirs, $file) {
  $dirs = (array) $dirs;
  $maps = array();
  foreach ($dirs as $dir) {
    $maps = array_merge($maps, static::createMap($dir));
  }
  file_put_contents($file, sprintf('<?php return %s;', var_export($maps, true)));
}