Add callbacks supporting generation and retrieval of supplemental data entries, facilitating RFC 5878 (TLS auth extensions)

Removed prior audit proof logic - audit proof support was implemented using the generic TLS extension API
Tests exercising the new supplemental data registration and callback api can be found in ssltest.c.
Implemented changes to s_server and s_client to exercise supplemental data callbacks via the -auth argument, as well as additional flags to exercise supplemental data being sent only during renegotiation.

apps/s_cb.c

@@ -876,6 +876,9 @@ void MS_CALLBACK msg_cb(int write_p, int version, int content_type, const void *
 				case 16:
 					str_details1 = ", ClientKeyExchange";
 					break;
+				case 23:
+					str_details1 = ", SupplementalData";
+					break;
 				case 20:
 					str_details1 = ", Finished";
 					break;