Implementation of soft dynamic time warping in pytorch

Here is my implementation of the Soft Dynamic Time Warping loss function described in https://arxiv.org/abs/1703.01541.

Currently I have only a 'naive' implementation without extending the fast cython implementation in https://github.com/mblondel/soft-dtw to incorporate a batch dimension. If I continue to use this in my line of research I may implement a cython / CUDA version to increase speed.

####### See: https://github.com/Maghoumi/pytorch-softdtw-cuda for a much better implementation #######