Ability to set a "reference" job

Right now when benchmarks are compared, they are always compared to the fastest run. I think it would be useful in some situations to set a "reference" run and compare all the other runs to that.

One example would be the benchmark suite of jason, where I'd like to see all the other encoders reported relative to Jason itself, even though jiffy is the fastest most of the time. Right now, I have to do the additional computations manually, to get the desired numbers, that I can use to annoy people convincing them how fast Jason is 😉.