Adding String.string-set!

Issue #94

core/String.carp

@@ -16,6 +16,7 @@
   (register from-chars (Fn [&(Array Char)] String))
   (register tail (λ [(Ref String)] String))
   (register format (Fn [&String &String] String))
+  (register string-set! (Fn [&String Int Char] ()))
 
   (defn /= [a b]
     (not (= (the (Ref String) a) b)))

core/carp_string.h

@@ -8,6 +8,10 @@ void String_delete(String s) {
     CARP_FREE(s);
 }
 
+void String_string_MINUS_set_BANG_(String *s, int i, char ch) {
+    (*s)[i] = ch;
+}
+
 String String_copy(String *s) {
     size_t len = strlen(*s) + 1;
     String ptr = CARP_MALLOC(len);