Add support of Eigen::Array

[jcarpent]

Currently, we only support so far Eigen::Matrix and Eigen::Map. It should be nice to extend the current API to also support Eigen::Array. This should be straightforward with the current setup.

[liangbright]

great work. can you also support sparse matrix so that we can use sparse linear system solvers? The input sparse matrix could be in the COO format, so a sparse matrix class is not needed as NumPy does not have one