[Feature Request] Comparing two functions

[SyxP]

One of the main uses I use BenchmarkTools.jl is to try to figure which of the two implementations I have are faster.

But my algorithms often would differ wildly on different pathological cases. I want to profile two functions with the same (random) sequence of inputs and do the statistic on the difference of times between function 1 and function 2.

[SyxP]

Whoops I only checked the docs not previous issues. Same as #283 and #239.