P fernbach topic/operator equal

See merge request loco-3d/curves!41

[CMake] update minimal eigenpy version

ref. https://github.com/stack-of-tasks/eigenpy/issues/126
cc. @stonneau

operator == : in child class, try to cast 'other' to the child type to perform the correct operation, before falling back to the curve_abc operator

Topic/piecewise generic