def []= index_or_hash, value
      index = index_or_hash
      if index_or_hash.is_a? Symbol
        index = table_header_keys.index(index_or_hash)
      elsif index_or_hash.is_a? String and index_or_hash.match(/^[A-Z]*$/)
        # it looks like a column indicator
        index = Workbook::Column.alpha_index_to_number_index(index_or_hash)
      elsif index_or_hash.is_a? String
        symbolized = Workbook::Cell.new(index_or_hash, {row:self}).to_sym
        index = table_header_keys.index(symbolized)
      end

      value_celled = Workbook::Cell.new
      if value.is_a? Workbook::Cell
        value_celled = value
      else
        current_cell = self[index]
        if current_cell.is_a? Workbook::Cell
          value_celled = current_cell
        end
        value_celled.value=(value)
      end
      value_celled.row = self
      super(index,value_celled)
    end
def []= index_or_hash, value
      index = index_or_hash
      if index_or_hash.is_a? Symbol
        index = table_header_keys.index(index_or_hash)
      elsif index_or_hash.is_a? String and index_or_hash.match(/^[A-Z]*$/)
        # it looks like a column indicator
        index = Workbook::Column.alpha_index_to_number_index(index_or_hash)
      elsif index_or_hash.is_a? String
        symbolized = Workbook::Cell.new(index_or_hash, {row:self}).to_sym
        index = table_header_keys.index(symbolized)
      end

      value_celled = Workbook::Cell.new
      if value.is_a? Workbook::Cell
        value_celled = value
      else
        current_cell = self[index]
        if current_cell.is_a? Workbook::Cell
          value_celled = current_cell
        end
        value_celled.value=(value)
      end
      value_celled.row = self
      super(index,value_celled)
    end
Overrides normal Array's []=-function with support for symbols that identify a column based on the header-values

 @example Lookup using fixnum or header value encoded as symbol (strings are converted to symbols)
   row[1] #=> <Cell value="a">
   row[:a] #=> <Cell value="a">

 @param [Fixnum, Symbol, String] index_or_hash that identifies the column
 @param [String, Fixnum, NilClass, Date, DateTime, Time, Float] value
 @return [Workbook::Cell, nil]