Correlate correlates benchmarks from two BenchSets.

BenchCmp is a pair of benchmarks.

Delta is the before and after value for a benchmark measurement.

ByDeltaAllocedBytesPerOp sorts BenchCmps lexicographically by change in B/op, descending, then by benchmark name.

ByDeltaAllocsPerOp sorts BenchCmps lexicographically by change in allocs/op, descending, then by benchmark name.

ByDeltaMBPerS sorts BenchCmps lexicographically by change in MB/s, descending, then by benchmark name.

ByDeltaNsPerOp sorts BenchCmps lexicographically by change in ns/op, descending, then by benchmark name.

ByParseOrder sorts BenchCmps to match the order in which the Before benchmarks were presented to Parse.