Debiasing for Tensorboard smoothing

[alexirpan]

This takes the existing smoothing algorithm, and updates it to avoid getting biased on the initial value. Addresses #610. At low smoothing values, the difference is small, but as smoothing approaches 1, the difference becomes clearer. At smoothing=1, the old code draws a straight line at data[0] - this code draws a straight line at 0 instead, just because of how the initialization changes.

Below are several pictures of the same curves with different smoothing values. The first image (teal curve) is before the change, and the second image (orange curve) is after the change.

Smoothing=0.0

Smoothing=0.1

Smoothing=0.6

Smoothing=0.9

Smoothing=0.999

Smoothing=1

[teamdandelion]

Thank you for this change, and for the clear before/after analysis on a number of different charts.