Suggest adding plugin `pheasant`

Auto Python code execution and insertion to the original Markdown source. Any Python codes in a fenced code block of original Markdown source are executed. This process is performed by a Jupyter client. In addition to this code execution, Pheasant can **automatically number headers, figures, tables, etc.** See the Pheasant official site at [Pheasant Home](https://pheasant.daizutabi.net/)