Add TorchScript

[leejuyuu]

This is my attempt to address the reviews of #113 .

[coveralls]

coverage: 100.0%. remained the same
when pulling e8c852e on leejuyuu:torchscriptable
into cc449eb on kmkurn:master.

[leejuyuu]

@kmkurn I rebased this onto the master branch.

[kmkurn]

Thank you for continuing the torchscript PR! Overall it looks good, but I left some requests and questions below.

One major request is about the structure of the tests. Do you mind changing it so that each assert is in its own test function/method? Similar to the tests for the non-scripted version. It will make pytest's report a lot clearer when a test fails. Feel free to create another test module under tests if necessary.

[leejuyuu]

I've split up the tests into smaller pieces. The commit messages are a bit messy, I think I'll squash them into one if it is ready to get merged.

[kmkurn]

Thanks for the changes and clarifications. It looks really good now. I just have a question and minor requests below before I can merge.

[kmkurn]

Thanks for the changes! Just a couple of minor requests from me, and the PR should be ready to merge.

[kmkurn]

I think this PR looks good to merge. If you still want to squash the commits into one, please do so now, and then let me know.

[leejuyuu]

@kmkurn Thanks! The commits are squashed into one.

[kmkurn]

Thank you for your contribution! The PR is now merged :-)