binc_device_stop_notify

[charlesnicholson]

There exists a function binc_device_start_notify but not the equivalent binc_device_stop_notify. For users to stop expressing interest in notifications on a specific characteristic, they had to use the functional-but-asymmetrical binc_characteristic_stop_notify function.

This PR adds a very simple binc_device_stop_notify method, for symmetry.

(If you don't want it, that's cool; the c'stic interface works just fine)

[weliem]

Thanks!