Function: to_lower

--Usage--
> to_lower(some_string)

Convert a string to lower case.

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

--Examples--
> to_lower("ABC")     == "abc"
> to_lower("123 aBc") == "123 abc"

--See also--
| [[fun:to_upper]]		Convert a string to upper case, @"aBc" -> "ABC"@.
| [[fun:to_title]]		Convert a string to title case, @"aBc" -> "Abc"@.
