code: function getFiles(env)
  {
    var files       = []
      , environment = env['NODE_ENV'] || this.defaults.environment
      , appInstance = env['NODE_APP_INSTANCE']
      ;
  
    // generate config files variations
    this.files.forEach(function(baseName)
    {
      // check for variables
      // keep baseName if no variables found
      baseName = parseTokens(baseName, env) || baseName;
  
      // add base name with available suffixes
      addWithSuffixes.call(this, files, baseName, appInstance);
      addWithSuffixes.call(this, files, baseName, environment, appInstance);
    }.bind(this));
  
    return files;
  }
docs: Creates list of files to load configuration from
  derived from the passed environment-like object
  
  @param   {object} env - environment-like object (e.g. `process.env`)
  @returns {array} - ordered list of config files to load