o Minor features:
   - Alter the Path Bias log messages to be more descriptive in terms
     of reporting timeouts and other statistics.
   - Create three levels of Path Bias log messages, as opposed to just
     two. These are configurable via consensus as well as via torrc
     options PathBiasNoticeRate, PathBiasWarnRate, PathBiasExtremeRate.
     The default values are 0.70, 0.50, and 0.30 respectively.
   - Separate the log message levels from the decision to drop guards,
     which also is available via torrc option PathBiasDropGuards.
     PathBiasDropGuards defaults to 0 (off).
   - Deprecate PathBiasDisableRate in favor of PathBiasDropGuards
     in combination with PathBiasExtremeRate.
   - Increase the default values for PathBiasScaleThreshold and
     PathBiasCircThreshold from 200 and 20 to 300 and 150, respectively.