tunnel msg spec update

www.i2p2/pages/tunnel-alt.html

@@ -106,38 +106,41 @@ fragments it across the necessary number of 1KB tunnel messages, and decides how
 each I2NP message should be handled by the tunnel endpoint, encoding that
 data into the raw tunnel payload:</p>
 <ul>
-<li>the first 4 bytes of the SHA256 of the remaining preprocessed data concatenated 
-    with the IV, using the IV as will be seen on the tunnel endpoint (for
-    outbound tunnels) or the IV as was seen on the tunnel gateway (for inbound
+<li>the first 4 bytes of the SHA256 of (the remaining preprocessed data concatenated 
+    with the IV), using the IV as will be seen on the tunnel endpoint (for
+    outbound tunnels), or the IV as was seen on the tunnel gateway (for inbound
     tunnels) (see below for IV processing).</li>
 <li>0 or more bytes containing random nonzero integers</li>
 <li>1 byte containing 0x00</li>
 <li>a series of zero or more { instructions, message } pairs</li>
 </ul>
 
+<p>Note that the padding, if any, must be before the instruction/message pairs.
+there is no provision for padding at the end.</p>
+
 <p>The instructions are encoded with a single control byte, followed by any
 necessary additional information.  The first bit in that control byte determines
 how the remainder of the header is interpreted - if it is not set, the message 
 is either not fragmented or this is the first fragment in the message.  If it is
 set, this is a follow on fragment.</p>
 
-<p>With the first bit being 0, the instructions are:</p>
+<p>With the first (leftmost or MSB) bit being 0, the instructions are:</p>
 <ul>
 <li>1 byte control byte:<pre>
       bit 0: is follow on fragment?  (1 = true, 0 = false, must be 0)
    bits 1-2: delivery type
              (0x0 = LOCAL, 0x01 = TUNNEL, 0x02 = ROUTER)
-      bit 3: delay included?  (1 = true, 0 = false)
+      bit 3: delay included?  (1 = true, 0 = false) (unimplemented)
       bit 4: fragmented?  (1 = true, 0 = false)
-      bit 5: extended options?  (1 = true, 0 = false)
+      bit 5: extended options?  (1 = true, 0 = false) (unimplemented)
    bits 6-7: reserved</pre></li>
 <li>if the delivery type was TUNNEL, a 4 byte tunnel ID</li>
 <li>if the delivery type was TUNNEL or ROUTER, a 32 byte router hash</li>
-<li>if the delay included flag is true, a 1 byte value:<pre>
+<li>if the delay included flag is true, a 1 byte value (unimplemented):<pre>
       bit 0: type (0 = strict, 1 = randomized)
    bits 1-7: delay exponent (2^value minutes)</pre></li>
 <li>if the fragmented flag is true, a 4 byte message ID</li>
-<li>if the extended options flag is true:<pre>
+<li>if the extended options flag is true (unimplemented):<pre>
    = a 1 byte option size (in bytes)
    = that many bytes</pre></li>
 <li>2 byte size of the I2NP message or this fragment</li>