Add a changelog entry for the circuit priority logic

Changes in version 0.2.2.7-alpha - 2009-??-??

  o Major features:

    - When choosing which cells to relay first, we can now favor circuits

      that have been quiet recently, so as to get lower latency for

      low-volume circuits.  By default, relays enable or disable this

      feature based on a setting in the consensus.  Preliminary testing

      suggests that this should make the network feel faster as more relays

      use it.  You can override this default by using the new

      "CircuitPriorityHalflife" config option.  Design and code by Ian

      Goldberg, Can Tang, and Chris Alexander.

  o Minor features:

    - New config option "CircuitStreamTimeout" to override our internal

      timeout schedule for how many seconds until we detach a stream from