o Major features (circuit padding):
    - Implement preliminary support for the circuit padding portion of
      Proposal 254. The implementation supports Adaptive Padding (aka
      WTF-PAD) state machines for use between experimental clients and
      relays. Support is also provided for APE-style state machines that
      use probability distributions instead of histograms to specify
      inter-packet delay. At the moment, Tor does not provide any padding
      state machines that are used in normal operation -- this feature
      exists solely for experimentation in this release. Closes
      ticket 28142.