Make argument handling more robust

[tbm]

./tp357tool.py
Traceback (most recent call last):
  File "/home/tbm/src/tp357/./tp357tool.py", line 139, in <module>
    device, read, write = bt_setup(sys.argv[1])
                                   ~~~~~~~~^^^
IndexError: list index out of range

It would be nice to show a help/usage message instead of a backtrace.

[tbm]

It thinks --help is the address.

./tp357tool.py --help                                                                                         main

(process:724756): GLib-GIO-CRITICAL **: 11:09:56.167: g_dbus_connection_call_sync_internal: assertion 'object_path != NULL && g_variant_is_object_path (object_path)' failed

(process:724756): GLib-GIO-CRITICAL **: 11:10:01.179: g_dbus_connection_call_sync_internal: assertion 'object_path != NULL && g_variant_is_object_path (object_path)' failed
Waiting for device... 1/12