I can open a PR for this, but thought it might be best to discuss it first as far as what should happen with None.

1. Raise an error that it's an incorrect call.
2. Ignore it and just return.
3. Loop through all the events and after_cancel each one. 

Tcl allows the after_cancel call to be an id or script(s), but they don't have functionality that would cancel everything (unless all the `script` values were sent).

FWIW, if no parameters are sent, this is the Tcl code:
	if (objc < 3) {
	    Tcl_WrongNumArgs(interp, 2, objv, "id|command");
	    return TCL_ERROR;
	}