Subflowchart-step

* Correctly pass loop exceptions, such as break and continue, that are raised in the
flowchart up to any loop that the subflowchart is in.
* Fixed issues with the redirection of printing if errors occur.

* Fixed the options, which were not being correctly handled for steps in the
subflowchart.

* This is the initial release of the plug-in.

* Plug-in created using the SEAMM plug-in cookiecutter.