common/json_stream.c: provide explicit json_add_primitive_fmt and json_add_str_fmt routines.

Rather than a generic "add member", provide two routines: one which
doesn't quote, and one which does.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

lightningd/options.c

@@ -1563,8 +1563,7 @@ static void add_config(struct lightningd *ld,
 			    || (!streq(buf, "") && strspn(buf, "0123456789.") == strlen(buf))) {
 				/* Let pure numbers and true/false through as
 				 * literals. */
-				json_add_literal(response, name0,
-						 buf, strlen(buf));
+				json_add_primitive(response, name0, buf);
 				return;
 			}