Optimize BitPat equals, overlap, and cover

[jackkoenig]

I also added some focused tests.

I am making this change because I noticed slow performance for a TruthTable that has 65k entries. The performance of just == on that TruthTable was pretty bad. Note that == for BitSet uses cover, so I first optimized that, then went ahead and also optimized equals, and then overlap was free so did that too. See benchmark for equality of two copies of a TruthTable with 65k entries:

Change	Runtime	Speedup over Baseline
Baseline	68 ms	-
Optimize cover	3.9 ms	17x
Optimize equals	1.3 ms	52x

There are other improvements to be made, but this is pretty good and constrained.

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• Did you add Scaladoc to every public function/method?
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• Performance improvement

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[chick]

LGTM