Use Krawczyk as default contractor ?

[Kolaru]

I have been playing around a bit and noticed that the Krawczyk contractor can be much faster than Newton (which is expected as it doesn't use an interval-valued jacobian). For example on the Smiley 5.5 example (4 dimensional):

julia> @time roots(SmileyExample55.f, X ; contractor = Newton) ;
173.267635 seconds (95.31 M allocations: 9.645 GiB, 2.81% gc time, 0.74% compilation time)

julia> @time roots(SmileyExample55.f, X ; contractor = Krawczyk) ;
 16.432576 seconds (8.03 M allocations: 673.482 MiB, 0.51% gc time, 3.66% compilation time)

Therefore, I am tempted to make Krawczyk the default for v1.0.

Is there any reason not to do so ? @dpsanders @lbenet @lucaferranti

[dpsanders]

I can't think of a reason not to do so off the top of my head. This idea had in fact already crossed my mind :) I say go ahead!