Return man page content for the given `cmdln.Cmdln` subclass name.

def mkmanpage(name):
    """Return man page content for the given `cmdln.Cmdln` subclass name."""
    mod_name, class_name = name.rsplit('.', 1)
    mod = __import__(mod_name)
    inst = getattr(mod, class_name)()
    sections = cmdln.man_sections_from_cmdln(inst)
    sys.stdout.write(''.join(sections))