Added support for the 'sign' op and its VJP.

[eaplatanios]

No description provided.

[rxwei]

Could you add a test for each of these operators?

[eaplatanios]

I can do that yes. I just noticed that there were no tests for other wrappers of TF ops. It would be nice if we added a little helper that executes XCTAssertEqual(_:_:accuracy:) element-wise on tensors. I could look into that later tonight.

[rxwei]

Yeah, other ops are mostly not tested. The migration made it so much easier to write tests now.

[eaplatanios]

I merged the matmul PR here (so I can get the test helpers) and added a test for sign. The diff once the matmul PR is merged should be very small. I'll do the same for the other new ops.

[eaplatanios]

@rxwei This has been updated with the merged PR changes and is ready to be tested. #142 is also ready to be tested.

[rxwei]

Kokoro seems back online. Thanks @bgogul for fixing it!

[rxwei]

Kokoro seems back online. Thanks @bgogul for fixing it!

@bgogul said he didn't do anything. Not sure what happened, Kokoro :)

[eaplatanios]

Haha yeah CI servers do that sometimes and it's so frustrating when they just don't trigger :)

[eaplatanios]

Hmm I'm not sure what's wrong in Kokoro but earlier it was showing that same log while tests were passing locally.

[rxwei]

All tests pass locally on my machine. Merging.