def margins=(margin)
      self::margin_left   = margin
      self::margin_right  = margin
      self::margin_top    = margin
      self::margin_bottom = margin
    end
def margins=(margin)
      self::margin_left   = margin
      self::margin_right  = margin
      self::margin_top    = margin
      self::margin_bottom = margin
    end
Set all the page margins to the same value in inches.

 There are several methods available for setting the worksheet margins
 on the printed page:

     margins=()                # Set all margins to the same value
     margins_left_right=()     # Set left and right margins to the same value
     margins_top_bottom=()     # Set top and bottom margins to the same value
     margin_left=()            # Set left margin
     margin_right=()           # Set right margin
     margin_top=()             # Set top margin
     margin_bottom=()          # Set bottom margin

 All of these methods take a distance in inches as a parameter.
 Note: 1 inch = 25.4mm. ;-) The default left and right margin is 0.7 inch.
 The default top and bottom margin is 0.75 inch. Note, these defaults
 are different from the defaults used in the binary file format
 by writeexcel gem.