Add FuncFlow support
Add support for running a sequence of funcs as specified
by the FuncFlow interface: PreRun->Run->PostRun
* PreRun(context.Context) ([]interface{}, error): runs prior to Run
* Run(context.Context, []interface{}) ([]interface{}, error): is
the main run func.
* PostRun(context.Context, []interface{}) error: runs after Run