code: function getPostPaths (dir) {
    return fs.readdir(dir).then(function (files) {
      return all(files.map(function (file) {
        var path = pathify(dir, file);
        return fs.stat(path).then(function (stats) {
          return stats.isDirectory() ?
            getPostPaths(path) :
            path;
        });
      }));
    }).then(function (files) {
      return _.flatten(files);
    });
  }
docs: Recursively search `dir` and return all file paths as strings in
  an array
  
  @params {String} dir
  @returns {Array}