changes file for the ntor branch

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+  o Major features:
+
+    - Tor now supports a new circuit extension handshake designed by Ian
+      Goldberg, Douglas Stebila, and Berkant Ustaoglu. Our original
+      circuit extension handshake, later called "TAP", was a bit slow
+      (especially on the server side), had a fragile security proof, and
+      used weaker keys than we'd now prefer. The new circuit handshake
+      uses Dan Bernstein's "curve25519" elliptic-curve Diffie-Hellman
+      function, making it significantly more secure than the older
+      handshake, and significantly faster. Tor can either use one of two
+      built-in pure-C curve25519-donna implementations by Adam Langley,
+      or link against the "nacl" library for a tuned version if present.
+
+      The built-in version is very fast for 64-bit systems building with
+      GCC. (About 10-14x faster on the server side, and about 7x faster
+      on the client side.) The built-in 32-bit version is still faster
+      than the old TAP protocol (about 3x), but using libnacl would be
+      better on most 32-bit x86 hosts.
+
+      Clients don't currently use this protocol by default, since
+      comparatively few clients support it so far. To try it, set
+      UseNTorHandshake to 1.
+
+      Implements proposal 216; closes ticket #7202.
+
+    - Tor servers and clients now support a better CREATE/EXTEND cell
+      format, allowing the sender to specify multiple address, identity,
+      and handshake types.  Implements Robert Ransom's proposal 200;
+      closes ticket #7199.
+
+  o Code simplification and refactoring:
+    - Split the onion.c file into separate modules for the onion queue
+      and the different handshakes it supports.
+    - Remove the marshalling/unmarshalling code for sending requests to
+      cpuworkers over a socket, and instead just send structs.  The
+      recipient will always be the same Tor binary as the sender, so
+      any encoding is overkill.
+
+  o Testing:
+    - Add benchmark functions to test onion handshake performance.