Function: english_plural

--Usage--
> english_plural(some_word)
> english_singular(some_word)

Convert a word to the plural or singular form.

--Parameters--
! Parameter	Type			Description
| @input@	[[type:string]]		String to convert

--Examples--
> english_plural("apple") == "apples"
> english_plural("berry") == "berries"
> english_singular("Red Horses") == "Red Horse"