Add ordinal functionality to format string

Ordinals often make dates more pleasant to read ('3rd', '14th'). I have used the format string character `E` because it is close to the normal date string (`e`), but also unused in Ruby (in std C it is a 'modifier', but according to the [Ruby documentation][1], it is ignored)

[1]: http://www.ruby-doc.org/core-2.1.1/Time.html#method-i-strftime