def add_rules(rules)
      rules = [rules] if rules.is_a? Hash
      rules.each do |rule|
        add_rule rule
      end
    end
Add Conditional Formatting Rules to this object. Rules can either
be already created {ConditionalFormattingRule} elements or
hashes of options for automatic creation.  If rules is a hash
instead of an array, assume only one rule being added.

@example This would apply formatting "1" to cells > 20, and formatting "2" to cells < 1
conditional_formatting.add_rules [
{ :type => :cellIs, :operator => :greaterThan, :formula => "20", :dxfId => 1, :priority=> 1 },
{ :type => :cellIs, :operator => :lessThan, :formula => "10", :dxfId => 2, :priority=> 2 } ]

@param [Array|Hash] rules the rules to apply, can be just one in hash form
@see ConditionalFormattingRule#initialize