code: function addPositions(base, relative) {
      return {
          line: base.line + relative.line - 1, // line 1 + line 1 should be line 1
          column: relative.line == 1 ? base.column + relative.column // when the same line
              : relative.column               // when another line
      };
  }
docs: add two positions.
  note: line starts with 1, column starts with 0.
  @param {Position} base
  @param {Position} relative
  @return {Position}