Adds ordinalize i.e. th,st,rd to a number for use in date string outputs

fixnum_ordinalize.rb

class Fixnum
  def ordinalize
    if (11..13).include?(self % 100)
      "#{self}th"
    else
      case self % 10
        when 1; "#{self}st"
        when 2; "#{self}nd"
        when 3; "#{self}rd"
        else    "#{self}th"
      end
    end
  end
end

From: http://stackoverflow.com/questions/1081926/how-do-i-format-a-date-in-ruby-to-include-rd-as-in-3rd

Doesn't work correctly for negative numbers. See my fork