Provide `difference` (`and_not`) and `symmetric_difference` (`xor`) operation

[uzytkownik]

I figure out I need to .not shape by finding issue #68. It would be nice if truck provided .not() operation even if for now they would be implemented in terms of .or and .and.

[ytanimura]

In boundary expressions, if one turns over all the faces of the shell, it's the same as doing a not operation. That's why I decided not to add it here, because I thought it wasn't something that should be listed in parallel. I might think about it again when it's a bit more complete.

[ytanimura]

Well, I'm sorry to say that I forgot, but the method not was defined directly in Solid.
https://docs.rs/truck-topology/0.6.0/truck_topology/struct.Solid.html#method.not

[uzytkownik]

I think it's most common for CADs to have difference and symmetric difference operations than negation. So I think many people will search for difference rather than not operation at first.