Write a bunch of module documentation.

This commit adds or improves the module-level documenation for:

  buffers.c circuitstats.c command.c connection_edge.c control.c
  cpuworker.c crypto_curve25519.c crypto_curve25519.h
  crypto_ed25519.c crypto_format.c dircollate.c dirserv.c dns.c
  dns_structs.h fp_pair.c geoip.c hibernate.c keypin.c ntmain.c
  onion.c onion_fast.c onion_ntor.c onion_tap.c periodic.c
  protover.c protover.h reasons.c rephist.c replaycache.c
  routerlist.c routerparse.c routerset.c statefile.c status.c
  tor_main.c workqueue.c

In particular, I've tried to explain (for each documented module)
what each module does, what's in it, what the big idea is, why it
belongs in Tor, and who calls it.  In a few cases, I've added TODO
notes about refactoring opportunities.

I've also renamed an argument, and fixed a few DOCDOC comments.

1 files changed, 11 insertions, 0 deletions

diff --git a/src/or/onion_ntor.c b/src/or/onion_ntor.c
index d1a268f4cd..ded97ee73d 100644
--- a/src/or/onion_ntor.c
+++ b/src/or/onion_ntor.c
@@ -5,6 +5,17 @@
  * \file onion_ntor.c
  *
  * \brief Implementation for the ntor handshake.
+ *
+ * The ntor circuit-extension handshake was developed as a replacement
+ * for the old TAP handshake.  It uses Elliptic-curve Diffie-Hellman and
+ * a hash function in order to perform a one-way authenticated key
+ * exchange.  The ntor handshake is meant to replace the old "TAP"
+ * handshake.
+ *
+ * We instantiate ntor with curve25519, HMAC-SHA256, and HKDF.
+ *
+ * This handshake, like the other circuit-extension handshakes, is
+ * invoked from onion.c.
  */
 
 #include "orconfig.h"