Merge pull request #365 from h2o/i110/add-quicint-max

define PTLS_QUICINT_MAX and PTLS_QUICINT_LONGEST_STR
diff --git a/include/picotls.h b/include/picotls.h
index 2486ff3..a25346a 100644
--- a/include/picotls.h
+++ b/include/picotls.h
@@ -947,6 +947,9 @@
 static uint8_t *ptls_encode_quicint(uint8_t *p, uint64_t v);
 #define PTLS_ENCODE_QUICINT_CAPACITY 8
 
+#define PTLS_QUICINT_MAX 4611686018427387903 // (1 << 62) - 1
+#define PTLS_QUICINT_LONGEST_STR "4611686018427387903"
+
 #define ptls_buffer_pushv(buf, src, len)                                                                                           \
     do {                                                                                                                           \
         if ((ret = ptls_buffer__do_pushv((buf), (src), (len))) != 0)                                                               \