Simpleflow

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- Enhancement/272/implement workflow cancelation (273)
- Bugfix: 270: signals improvements (271)
- Enhancement: timer: get_event_details (269)
- Append "/" to get_step_path_prefix (268)
- Enhancement/misc (266)
- Repair reruns successful child workflows (191)

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- Feature: timers (258)

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- Kill worker on UnknownResourceFault's during a heartbeat (88) (263)
- Sort keys by default in json_dumps (264)

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- Fix step attribute propagation (261)
- Enhancement: get_event_details (235)

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- Enhancement: distinguish raises_on_failure between tasks and groups (255)
- Add time constants
- Relax activity.with_attributes timeouts types

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- Enhancement: add canvas option break_on_failure (253)
- Compute task_id from ActivityTask if has get_task_id method (237)
- Another case of wrong task list (234)