CHOLMOD supports this, it just wasn't exposed in the interface.
It is needed for large problems.

And fix all spelling errors that codespell currently finds.

See https://reuse.software/ for a description.

See discussion at !460

Both behave like std::tuple, and currently even inherit from std::tuple.
According to

  https://en.cppreference.com/w/cpp/utility/tuple_element

we are allowed to specify std::tuple_element for our own types.

This is needed for some of the more advanced features of CHOLMOD.

Fixes #91

This is achieved by using the flat matrix and vector forEach implementations.
The unit test is extended by a multi type example.

The routines traverse the container recursively and call a functor
at each scalar entry passing also the flat index.