Devices and Streams

Device	A device to run operations on.
Stream	A stream for running operations on a given device.
default_device()	Get the default device.
set_default_device(device)	Set the default device.
default_stream(device)	Get the device's default stream.
new_stream(device)	Make a new stream on the given device.
set_default_stream(stream)	Set the default stream.
stream(s)	Create a context manager to set the default device and stream.