Function: to_upper

--Usage--
> to_upper(some_string)

Convert a string to upper case.

--Parameters--
| @input@	[[type:string]]		String to convert.

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

--See also--
| [[fun:to_lower]]		Convert a string to lower case, @"aBc" -> "abc"@.
| [[fun:to_title]]		Convert a string to title case, @"aBc" -> "Abc"@.
