code: function relativePath(from, to) {
    // console.log('relativePath:from: ' + from);
    // console.log('relativePath:to: ' + to);
    var relative = path.relative(from, to);
    if (!relative || relative.length < 1) {
      return relative;
    }
    var first = relative.substr(0, 1);
    if (first !== '.' && first !== '/') {
      relative = './' + relative;
    }
  
    // especially used for windows
    relative = relative.split(path.sep).join('/');
  
    return relative;
  }
docs: get relative path
  
  @param from
  @param to
  @returns {*}