Add the approximate verification and solving.

[vletard]

Approximate verification and solving allow analogical computing to output solutions that are not quite correct with a deviation measure for estimating the number of approximations that was necessary.
This is useful for computing analogies with sparse data but comes with a very high computing cost. This issue should be very carefully designed in order to limit the actual CPU and memory usage and/or offer control/tracking info over the execution to the user.