Direct access to uint16 values in HalfStorage

[pdevine]

When I'm using the pytorch interface and getting HalfStorage (i.e. 16 bit float values) I'd like to be able to get access to the underlying []uint16 data instead of having it convert to []float32.

The way it's written I have to take the float32 values and convert them back into uint16 which results in a lot of unnecessary conversions.