Datarunner

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* Convert to str before checking for value

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* Add special var to strip hyphen from replacement values

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* Support passing optional args to steps

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* Merge existing flow before extend

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* Add extend to extend a list of steps to workflow

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* Add use of lshift to readme and tests
* Change Flow and Workflow to inherit from list only
* Support setting name for workflow
* Update package URL
* Better wording for recommended layout
* Add _merge_flow to avoid duplicating code