Have type_caster for Eigen::Map create its own temp array

[ManifoldFR]

This PR:

• Has type_caster<Eigen::Map<...>> create its own copy of the input NDArray
  • with appropriate strides,
  • pointing to data with same lifetime as the function (using the cleanup_list *cleanup arg in from_python).
  • This will only happen when the inner stride is 1 (maybe we can handle other strides later?), otherwise the caster will return false (Eigen::Ref will then dispatch to the Map type caster with dynamic strides and rely on its constructor creating an internal copy Ref::m_object, which was the previous behaviour)
• adds a test to test_eigen.cpp|test_eigen.py which tests a function with argument std::vector<Eigen::Ref<const VectorXd>>, which creates a temp copy when an array with the wrong order is given.

Fixes #682

[wjakob]

This is a rather intrusive change given that it's only needed to work around a defect in Eigen that has since been fixed. I'm inclined to rather detect the conditions where a problem could occur at compile time, and to then inform the user that they need to update their Eigen version.

Another opinion would be useful -- do you have thoughts on this @WKarel?

[WKarel]

#682 (comment)