Added string formatting library

[Izaakwltn]

Here is a rough draft for a string formatting library.

I'm happy to change any of the names or syntax.

The library centers around a macro format, which takes any number of strings and concatenates them into one string.

The rest of the library provides tools for formatting different types into strings in different ways.

A few examples:

COALTON-LIBRARY/FORMAT> (coalton (format "Numbers:" \n (format-with-delimiter eng \n (iter:up-to 5))))
"Numbers:
zero
one
two
three
four
"

COALTON-LIBRARY/FORMAT> (coalton (format "the number " (ticked 20) " is not the same as " (ticked 21)))
"the number `20` is not the same as `21`"

COALTON-LIBRARY/FORMAT> (coalton-toplevel
                          (declare print-bin (Integer -> Unit))
                          (define (print-bin x)
                            (coalton-library/functions:trace (format "The integer " (into x) " is printed in binary as " (bin x)))))
; No value
COALTON-LIBRARY/FORMAT> (coalton (print-bin 3))
The integer 3 is printed in binary as 11