A Fibonacci fitter is useful in situations where you want more precision on the
low end than an ExponentialFitter with exponent base 2 provides without the
hassle of dealing with non-integer boundaries, such as would be created by an
exponential fitter with a base of less than 2. Fibonacci fitters are ideal for
integer metrics that are bounded across a certain range, e.g. integers between 1
and 1,000.
This also cleans up some unit test comments.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=156773367
