support ptpython

[William Stein]

This https://github.com/prompt-toolkit/ptpython/ is pretty amazing in terms of interactive editing of the past, etc. See https://www.terriblecode.com/blog/why-ptpython-is-the-only-repl-you-will-ever-need/

There's also pyvim, which might also be a very interesting way to get something close to vim in the browser... but maybe not.
Unclear: https://pypi.org/project/pyvim/