Docs, code cleanup, and protect the extra new fields of HELLO with encryption as a precaution.

node/Constants.hpp

@@ -293,6 +293,11 @@
  */
 #define ZT_PEER_PATH_EXPIRATION ((ZT_PEER_PING_PERIOD * 4) + 3000)
 
+/**
+ * Send a full HELLO every this often (ms)
+ */
+#define ZT_PEER_SEND_FULL_HELLO_EVERY (ZT_PEER_PING_PERIOD * 2)
+
 /**
  * How often to retry expired paths that we're still remembering
  */