Merge TB_EMPTY events, take out [OR_]TOKENS events.

         "STATUS_CLIENT" / "STATUS_SERVER" / "GUARD" / "NS" / "STREAM_BW" /

         "CLIENTS_SEEN" / "NEWCONSENSUS" / "BUILDTIMEOUT_SET" / "SIGNAL" /

         "CONF_CHANGED" / "CIRC_MINOR" / "CONN_BW" / "CELL_STATS" /

         "TOKENS" / "OR_TOKENS" / "TB_EMPTY"

         "TB_EMPTY"

  Any events *not* listed in the SETEVENTS line are turned off; thus, sending

  SETEVENTS with an empty body turns off all event reporting.

4.1.22. Token buckets refilled

  The syntax is:

     "650" SP "TOKENS" SP

        GlobalReadBefore SP GlobalReadAfter SP

        GlobalWriteBefore SP GlobalWriteAfter SP

        RelayReadBefore SP RelayReadAfter SP

        RelayWriteBefore SP RelayWriteAfter CRLF

  GlobalReadBefore (GlobalWriteBefore) is the number of tokens in the

  global read (write) bucket before refilling, GlobalReadAfter

  (GlobalWriteAfter) is the number of tokens after refilling.

  RelayReadBefore (RelayWriteBefore) is the number of tokens in the relay

  read (write) bucket before refilling, RelayReadAfter (RelayWriteAfter)

  is the number of tokens after refilling.

  The syntax for a related event is:

     "650" SP "TB_EMPTY" SP ["GLOBAL" || "RELAY"] SP

     "650" SP "TB_EMPTY" SP ["GLOBAL" || "RELAY" || "ORCONN" SP ConnID] SP

        ReadBucketEmpty SP WriteBucketEmpty SP LastRefill CRLF

  The "GLOBAL" keyword is used when one of the global buckets runs out of

  tokens, and the "RELAY" keyword is used when one of the relay buckets

  runs out of tokens.  If both global and relay buckets run out of tokens

  at the same time, two separate events are generated.

  This even is generated when refilling a previously empty token bucket.

  The "GLOBAL" and "RELAY" keywords are used for the global or relay token

  buckets, the "ORCONN" keyword together with a ConnID is used for the

  token buckets of an OR connection.

  ReadBucketEmpty (WriteBucketEmpty) is the time in millis that the read

  (write) bucket was empty.  LastRefill is the time in millis since the

  last refill.  ReadBucketEmpty or WriteBucketEmpty are capped at

  LastRefill in order not to report empty times more than once.

  These events are generated whenever token buckets are refilled, but only

  if TestingTorNetwork is set.  The "TB_EMPTY" event is only generated if

  a bucket was empty before refilling.

 4.1.23. Per-connection token buckets refilled

  The syntax is:

     "650" SP "OR_TOKENS" SP ConnID SP ReadBefore SP ReadAfter SP

        WriteBefore SP WriteAfter CRLF

  ConnID is the connection ID of this OR connection.

  ReadBefore (WriteBefore) is the number of tokens in the connection read

  (write) bucket before refilling, ReadAfter (WriteAfter) is the number of

  tokens after refilling.

  The syntax for a related event is:

     "650" SP "TB_EMPTY" SP "ORCONN" SP ConnID SP ReadBucketEmpty SP

        WriteBucketEmpty SP LastRefill CRLF

  ConnID is the connection ID of this OR connection.

  If both global and relay buckets and/or the buckets of one or more OR

  connections run out of tokens at the same time, multiple separate events

  are generated.

  ReadBucketEmpty (WriteBucketEmpty) is the time in millis that the read

  (write) bucket was empty.  LastRefill is the time in millis since the

  last refill.  ReadBucketEmpty or WriteBucketEmpty are capped at

  LastRefill in order not to report empty times more than once.

  These events are generated whenever token buckets are refilled and for

  every OR connection that had its buckets refilled, but only if

  TestingTorNetwork is set.  The "TB_EMPTY" event is only generated if

  a bucket was empty before refilling.

  These events are only generated if TestingTorNetwork is set.

5. Implementation notes