Add intro.ts demo that demos intro tutorial, fix intro to actually converge when training.

[nsthorat]

This change is 

Fixes #22

[dsmilkov]

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Review status: 0 of 3 files reviewed at latest revision, 4 unresolved discussions.

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demos/intro/index.html, line 1 at r1 (raw file):

<h1>Introduction tutorial code</h1>

Add copyright header

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demos/intro/intro.ts, line 39 at r1 (raw file):

    // Blocking call to actually read the values from average. Waits until the
    // GPU has finished executing the operations before returning values.
    console.log('mean squared difference: ' + average.get());  // average is a Scalar so we use .get()

wrap to 80 width

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demos/intro/intro.ts, line 58 at r1 (raw file):

  const labelTensor = g.placeholder('label', labelShape);

  // Variables are containers that hold a value that can be updated from training.

wrap line

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demos/intro/intro.ts, line 133 at r1 (raw file):

    console.log('value: ' + testOutput.get(0));
  });
}

should we dispose all inputs and labels here? or too much detail for this tutorial?

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