def headers(row = nil)
      row ||= rows.first
      header_type = row.th.exist? ? 'th' : 'td'
      row.send("#{header_type}s")
    end
def headers(row = nil)
      row ||= rows.first
      header_type = row.th.exist? ? 'th' : 'td'
      row.send("#{header_type}s")
    end
Returns first row of Table with proper subtype

 @return [TableCellCollection]