neo_doxygen: Add an option to remove the `def` keyword of Python.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>
neo_doxygen: Include a tip for Python in the `README`.

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>