Add `%q` for runes in fmt

core/fmt/fmt.odin

@@ -776,6 +776,8 @@ fmt_rune :: proc(fi: ^Info, r: rune, verb: rune) {
 	switch verb {
 	case 'c', 'r', 'v':
 		strings.write_rune(fi.buf, r);
+	case 'q':
+		strings.write_quoted_rune(fi.buf, r);
 	case:
 		fmt_int(fi, u64(r), false, 32, verb);
 	}

core/strings/builder.odin

@@ -131,6 +131,22 @@ write_rune :: proc(b: ^Builder, r: rune) -> int {
 	return n;
 }
 
+write_quoted_rune :: proc(b: ^Builder, r: rune) -> (n: int) {
+	quote := byte('\'');
+	n += write_byte(b, quote);
+	buf, width := utf8.encode_rune(r);
+	if width == 1 && r == utf8.RUNE_ERROR {
+		n += write_byte(b, '\\');
+		n += write_byte(b, 'x');
+		n += write_byte(b, DIGITS_LOWER[buf[0]>>4]);
+		n += write_byte(b, DIGITS_LOWER[buf[0]&0xf]);
+	} else {
+		n += write_escaped_rune(b, r, quote);
+	}
+	n += write_byte(b, quote);
+	return;
+}
+
 write_string :: proc(b: ^Builder, s: string) -> (n: int) {
 	return write_bytes(b, transmute([]byte)s);
 }