Acknowledge the existence of cpu HalfTensor (pytorch#2018)

Author: narendasan

docs/source/tensors.rst

@@ -13,7 +13,7 @@ Data type                CPU tensor                    GPU tensor
 ======================== ===========================   ================================
 32-bit floating point    :class:`torch.FloatTensor`    :class:`torch.cuda.FloatTensor`
 64-bit floating point    :class:`torch.DoubleTensor`   :class:`torch.cuda.DoubleTensor`
-16-bit floating point    N/A                           :class:`torch.cuda.HalfTensor`
+16-bit floating point    :class:`torch.HalfTensor`     :class:`torch.cuda.HalfTensor`
 8-bit integer (unsigned) :class:`torch.ByteTensor`     :class:`torch.cuda.ByteTensor`
 8-bit integer (signed)   :class:`torch.CharTensor`     :class:`torch.cuda.CharTensor`
 16-bit integer (signed)  :class:`torch.ShortTensor`    :class:`torch.cuda.ShortTensor`