chore: move validation to examples (#67)

**Summary**
This PR removes the validation subdirectory and moves its content to
example.

I initially felt like a validation subdir had some sense, as it shows
that the code actually does what it should.
With #65 that adds a thorough example, I feel like it makes more sense
to put everything as examples.

Maybe at some point add a README to explain that the results were
validated, with a link to the LJ mixture example?

Author: V-Francois