get_devices() returns a list of device names registered by the
given user
is.registered_ device() returns a logical value for each of the
given devices that indicates whether or not that device is registered to the
given user.
# NOT RUN {get_devices(
user = "uQiRzpo4DXghDmr9QzzfQu27cmVRsG",
app = "azGDORePK8gMaC0QOYAMyEEuzJnyUi")
# }# NOT RUN {is.registered_device(device = "phone")
# }