Function: format

--Usage--
> format(some_number, format: format_specification)
> format_rule(format: format_specification)(some_number)

Format a number or other string as a string, [[http://www.cplusplus.com/reference/clibrary/cstdio/printf.html|printf]] style.
This function is available in [[script:rule form]].

--Parameters--
| @input@	[[type:int]] or [[type:double]] or [[type:string]]
		  			Item to format.
| @format@	[[type:string]]		Format specification.

--Examples--
> format(format: "%03X", 13)    ==  "00D"
> format(format: "%03d", 13)    ==  "013"
> format(format: "%3s",  "xy")  ==  " xy"
>
> f := format_rule(format: "%03d")
> f(1) == "001"
