Add `unify` keyword and default if to `true`

[Suavesito-Olimpiada]

fix #48

[Suavesito-Olimpiada]

Still to add tests and discuss the proper algorithm to unify boxes.

[lucaferranti]

Out of curiosity, do you know how much computational overhead this introduces? Just wondering which one would be a better default value.

Here a simple MWE that might be good for benchmarking

julia> f(x) = x^2 - 2x + 1
f (generic function with 1 method)

julia> minval, minimisers = minimise(f, 0..2, tol=1e-6)

this example should return 2990 minimisers, so it might be a good small but not too small example for benchmarking

[lucaferranti]

Ah, you answered my questions while I was writing that 😄 Amazing! sorry for the noise

[Suavesito-Olimpiada]

Don't worry, happy to help. :D

[dpsanders]

At a first glance this looks great, thanks! Could you please add some tests?

[Suavesito-Olimpiada]

Sure, I'll add test. I just want to know what do you think about the "problem" of using union-find that I described in the comment in the original issue.