def initialize(options={})
      # Default values taken from MS Excel for Mac 2011
      @left = @right = DEFAULT_LEFT_RIGHT
      @top = @bottom = DEFAULT_TOP_BOTTOM
      @header = @footer = DEFAULT_HEADER_FOOTER
      parse_options options
    end
Creates a new PageMargins object
@option options [Numeric] left The left margin in inches
@option options [Numeric] right The right margin in inches
@option options [Numeric] bottom The bottom margin in inches
@option options [Numeric] top The top margin in inches
@option options [Numeric] header The header margin in inches
@option options [Numeric] footer The footer margin in inches