• Report a more user-friendly error if an action-chain task references an invalid or inexistent
  action. Also treat invalid / inexistent action as a top-level action-chain error. (improvement)
• Report a more user-friendly error if an action-chain definition contains an invalid type.
  (improvement)
• Enable authentication by default for package based installations.
• Rename all st2 processes to be prefixed by st2. (sensor_container is now st2sensorcontainer,
  rules_engine is now st2rulesengine, actionrunner is now st2actionrunner) (improvement)
• Return a user friendly error on no sensors found or typo in sensor class name in single
  sensor mode. (improvement)
• Sensor container now returns non-zero exit codes for errors. (bug-fix)
• Check if internal trigger types are already registered before registering
  them again. (improvement)
• Sensor container now can dynamically load/reload/unload sensors on data model changes.
  (new-feature)
• Fix a bug in datastore operations exposed in st2client. (bug-fix)
• Catch exception if rule operator functions throw excepton and ignore the rule. (bug-fix)
• Remove expected "runnertype not found" error logs on action registration
  in clean db. (improvement)
• Clean up rule registrar logging. (improvement)
• Add -t / --only-token flag to the st2 auth command. (new-feature)
• register param in packs.install should be passed to packs.load. (bug-fix)
• Fix validation code to validate value types correctly. (bug-fix)
• Add ability to best-effort cancel actions and actionchain via API. (new-feature)
• Add new windows-cmd and windows-script runners for executing commands
  and PowerShell scripts on Windows hosts. (new-feature)
• Update runner names so they follow a consistent naming pattern. For backward
  compatibility reasons, runners can still be referenced using their old names.
  (improvement)
• Update all the Python services to re-open log files on the SIGUSR1 signal. (new-feature)
• Internal trigger types registered using APIs should use auth token. (bug-fix)