Need API for saving to file.

[sanyam5]

Currently we only have a load function. But after training the network it would be great if we can save the generated tensor to a file.

@soumith I think we can reuse a lot of code from this repo https://github.com/MattVitelli/GRUV

[SeanNaren]

Added the ability in the PR #3, check the branch if you want to start loading audio till its merged!