def insert_line(index, item = [])
      fail(LineInsertOutOfBounds, "#{num} is higher then #{lines}") if index > @lines.length
      @lines.insert(index + @offset_y, LineBuffer.new(item))
      update_highlighter
    end
def insert_line(index, item = [])
      fail(LineInsertOutOfBounds, "#{num} is higher then #{lines}") if index > @lines.length
      @lines.insert(index + @offset_y, LineBuffer.new(item))
      update_highlighter
    end
Insert a new line at index, throws a {Mad::LineInsertOutOfBounds} exception if the index is higher
 than the current amount of lines

 @note Updates the highlighter (costly) see {#update_highlighter #update_highlighter}
 @param index [Fixnum] the index to insert at
 @param item [Array<String>] array of characters to insert
 @return [void]